![Kiyoshi Ueda](/assets/img/avatar_default.png)
This patch adds an new interface, blk_lld_busy(), to check lld's busy state from the block layer. blk_lld_busy() calls down into low-level drivers for the checking if the drivers set q->lld_busy_fn() using blk_queue_lld_busy(). This resolves a performance problem on request stacking devices below. Some drivers like scsi mid layer stop dispatching request when they detect busy state on its low-level device like host/target/device. It allows other requests to stay in the I/O scheduler's queue for a chance of merging. Request stacking drivers like request-based dm should follow the same logic. However, there is no generic interface for the stacked device to check if the underlying device(s) are busy. If the request stacking driver dispatches and submits requests to the busy underlying device, the requests will stay in the underlying device's queue without a chance of merging. This causes performance problem on burst I/O load. With this patch, busy state of the underlying device is exported via q->lld_busy_fn(). So the request stacking driver can check it and stop dispatching requests if busy. The underlying device driver must return the busy state appropriately: 1: when the device driver can't process requests immediately. 0: when the device driver can process requests immediately, including abnormal situations where the device driver needs to kill all requests. Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
471 lines
14 KiB
C
471 lines
14 KiB
C
/*
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* Functions related to setting various queue properties from drivers
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/init.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/bootmem.h> /* for max_pfn/max_low_pfn */
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#include "blk.h"
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unsigned long blk_max_low_pfn;
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EXPORT_SYMBOL(blk_max_low_pfn);
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unsigned long blk_max_pfn;
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/**
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* blk_queue_prep_rq - set a prepare_request function for queue
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* @q: queue
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* @pfn: prepare_request function
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*
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* It's possible for a queue to register a prepare_request callback which
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* is invoked before the request is handed to the request_fn. The goal of
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* the function is to prepare a request for I/O, it can be used to build a
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* cdb from the request data for instance.
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*
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*/
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void blk_queue_prep_rq(struct request_queue *q, prep_rq_fn *pfn)
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{
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q->prep_rq_fn = pfn;
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}
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EXPORT_SYMBOL(blk_queue_prep_rq);
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/**
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* blk_queue_set_discard - set a discard_sectors function for queue
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* @q: queue
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* @dfn: prepare_discard function
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*
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* It's possible for a queue to register a discard callback which is used
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* to transform a discard request into the appropriate type for the
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* hardware. If none is registered, then discard requests are failed
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* with %EOPNOTSUPP.
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*
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*/
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void blk_queue_set_discard(struct request_queue *q, prepare_discard_fn *dfn)
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{
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q->prepare_discard_fn = dfn;
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}
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EXPORT_SYMBOL(blk_queue_set_discard);
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/**
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* blk_queue_merge_bvec - set a merge_bvec function for queue
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* @q: queue
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* @mbfn: merge_bvec_fn
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*
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* Usually queues have static limitations on the max sectors or segments that
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* we can put in a request. Stacking drivers may have some settings that
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* are dynamic, and thus we have to query the queue whether it is ok to
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* add a new bio_vec to a bio at a given offset or not. If the block device
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* has such limitations, it needs to register a merge_bvec_fn to control
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* the size of bio's sent to it. Note that a block device *must* allow a
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* single page to be added to an empty bio. The block device driver may want
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* to use the bio_split() function to deal with these bio's. By default
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* no merge_bvec_fn is defined for a queue, and only the fixed limits are
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* honored.
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*/
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void blk_queue_merge_bvec(struct request_queue *q, merge_bvec_fn *mbfn)
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{
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q->merge_bvec_fn = mbfn;
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}
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EXPORT_SYMBOL(blk_queue_merge_bvec);
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void blk_queue_softirq_done(struct request_queue *q, softirq_done_fn *fn)
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{
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q->softirq_done_fn = fn;
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}
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EXPORT_SYMBOL(blk_queue_softirq_done);
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void blk_queue_rq_timeout(struct request_queue *q, unsigned int timeout)
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{
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q->rq_timeout = timeout;
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}
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EXPORT_SYMBOL_GPL(blk_queue_rq_timeout);
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void blk_queue_rq_timed_out(struct request_queue *q, rq_timed_out_fn *fn)
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{
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q->rq_timed_out_fn = fn;
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}
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EXPORT_SYMBOL_GPL(blk_queue_rq_timed_out);
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void blk_queue_lld_busy(struct request_queue *q, lld_busy_fn *fn)
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{
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q->lld_busy_fn = fn;
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}
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EXPORT_SYMBOL_GPL(blk_queue_lld_busy);
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/**
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* blk_queue_make_request - define an alternate make_request function for a device
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* @q: the request queue for the device to be affected
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* @mfn: the alternate make_request function
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*
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* Description:
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* The normal way for &struct bios to be passed to a device
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* driver is for them to be collected into requests on a request
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* queue, and then to allow the device driver to select requests
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* off that queue when it is ready. This works well for many block
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* devices. However some block devices (typically virtual devices
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* such as md or lvm) do not benefit from the processing on the
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* request queue, and are served best by having the requests passed
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* directly to them. This can be achieved by providing a function
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* to blk_queue_make_request().
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*
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* Caveat:
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* The driver that does this *must* be able to deal appropriately
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* with buffers in "highmemory". This can be accomplished by either calling
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* __bio_kmap_atomic() to get a temporary kernel mapping, or by calling
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* blk_queue_bounce() to create a buffer in normal memory.
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**/
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void blk_queue_make_request(struct request_queue *q, make_request_fn *mfn)
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{
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/*
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* set defaults
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*/
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q->nr_requests = BLKDEV_MAX_RQ;
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blk_queue_max_phys_segments(q, MAX_PHYS_SEGMENTS);
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blk_queue_max_hw_segments(q, MAX_HW_SEGMENTS);
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q->make_request_fn = mfn;
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q->backing_dev_info.ra_pages =
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(VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
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q->backing_dev_info.state = 0;
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q->backing_dev_info.capabilities = BDI_CAP_MAP_COPY;
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blk_queue_max_sectors(q, SAFE_MAX_SECTORS);
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blk_queue_hardsect_size(q, 512);
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blk_queue_dma_alignment(q, 511);
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blk_queue_congestion_threshold(q);
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q->nr_batching = BLK_BATCH_REQ;
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q->unplug_thresh = 4; /* hmm */
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q->unplug_delay = (3 * HZ) / 1000; /* 3 milliseconds */
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if (q->unplug_delay == 0)
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q->unplug_delay = 1;
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INIT_WORK(&q->unplug_work, blk_unplug_work);
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q->unplug_timer.function = blk_unplug_timeout;
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q->unplug_timer.data = (unsigned long)q;
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/*
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* by default assume old behaviour and bounce for any highmem page
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*/
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blk_queue_bounce_limit(q, BLK_BOUNCE_HIGH);
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}
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EXPORT_SYMBOL(blk_queue_make_request);
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/**
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* blk_queue_bounce_limit - set bounce buffer limit for queue
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* @q: the request queue for the device
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* @dma_addr: bus address limit
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*
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* Description:
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* Different hardware can have different requirements as to what pages
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* it can do I/O directly to. A low level driver can call
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* blk_queue_bounce_limit to have lower memory pages allocated as bounce
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* buffers for doing I/O to pages residing above @dma_addr.
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**/
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void blk_queue_bounce_limit(struct request_queue *q, u64 dma_addr)
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{
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unsigned long b_pfn = dma_addr >> PAGE_SHIFT;
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int dma = 0;
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q->bounce_gfp = GFP_NOIO;
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#if BITS_PER_LONG == 64
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/* Assume anything <= 4GB can be handled by IOMMU.
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Actually some IOMMUs can handle everything, but I don't
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know of a way to test this here. */
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if (b_pfn < (min_t(u64, 0x100000000UL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
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dma = 1;
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q->bounce_pfn = max_low_pfn;
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#else
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if (b_pfn < blk_max_low_pfn)
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dma = 1;
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q->bounce_pfn = b_pfn;
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#endif
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if (dma) {
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init_emergency_isa_pool();
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q->bounce_gfp = GFP_NOIO | GFP_DMA;
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q->bounce_pfn = b_pfn;
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}
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}
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EXPORT_SYMBOL(blk_queue_bounce_limit);
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/**
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* blk_queue_max_sectors - set max sectors for a request for this queue
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* @q: the request queue for the device
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* @max_sectors: max sectors in the usual 512b unit
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*
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* Description:
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* Enables a low level driver to set an upper limit on the size of
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* received requests.
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**/
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void blk_queue_max_sectors(struct request_queue *q, unsigned int max_sectors)
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{
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if ((max_sectors << 9) < PAGE_CACHE_SIZE) {
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max_sectors = 1 << (PAGE_CACHE_SHIFT - 9);
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printk(KERN_INFO "%s: set to minimum %d\n",
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__func__, max_sectors);
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}
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if (BLK_DEF_MAX_SECTORS > max_sectors)
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q->max_hw_sectors = q->max_sectors = max_sectors;
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else {
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q->max_sectors = BLK_DEF_MAX_SECTORS;
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q->max_hw_sectors = max_sectors;
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}
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}
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EXPORT_SYMBOL(blk_queue_max_sectors);
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/**
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* blk_queue_max_phys_segments - set max phys segments for a request for this queue
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* @q: the request queue for the device
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* @max_segments: max number of segments
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*
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* Description:
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* Enables a low level driver to set an upper limit on the number of
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* physical data segments in a request. This would be the largest sized
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* scatter list the driver could handle.
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**/
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void blk_queue_max_phys_segments(struct request_queue *q,
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unsigned short max_segments)
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{
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if (!max_segments) {
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max_segments = 1;
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printk(KERN_INFO "%s: set to minimum %d\n",
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__func__, max_segments);
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}
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q->max_phys_segments = max_segments;
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}
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EXPORT_SYMBOL(blk_queue_max_phys_segments);
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/**
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* blk_queue_max_hw_segments - set max hw segments for a request for this queue
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* @q: the request queue for the device
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* @max_segments: max number of segments
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*
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* Description:
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* Enables a low level driver to set an upper limit on the number of
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* hw data segments in a request. This would be the largest number of
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* address/length pairs the host adapter can actually give at once
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* to the device.
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**/
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void blk_queue_max_hw_segments(struct request_queue *q,
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unsigned short max_segments)
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{
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if (!max_segments) {
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max_segments = 1;
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printk(KERN_INFO "%s: set to minimum %d\n",
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__func__, max_segments);
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}
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q->max_hw_segments = max_segments;
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}
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EXPORT_SYMBOL(blk_queue_max_hw_segments);
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/**
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* blk_queue_max_segment_size - set max segment size for blk_rq_map_sg
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* @q: the request queue for the device
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* @max_size: max size of segment in bytes
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*
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* Description:
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* Enables a low level driver to set an upper limit on the size of a
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* coalesced segment
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**/
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void blk_queue_max_segment_size(struct request_queue *q, unsigned int max_size)
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{
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if (max_size < PAGE_CACHE_SIZE) {
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max_size = PAGE_CACHE_SIZE;
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printk(KERN_INFO "%s: set to minimum %d\n",
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__func__, max_size);
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}
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q->max_segment_size = max_size;
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}
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EXPORT_SYMBOL(blk_queue_max_segment_size);
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/**
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* blk_queue_hardsect_size - set hardware sector size for the queue
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* @q: the request queue for the device
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* @size: the hardware sector size, in bytes
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*
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* Description:
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* This should typically be set to the lowest possible sector size
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* that the hardware can operate on (possible without reverting to
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* even internal read-modify-write operations). Usually the default
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* of 512 covers most hardware.
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**/
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void blk_queue_hardsect_size(struct request_queue *q, unsigned short size)
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{
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q->hardsect_size = size;
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}
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EXPORT_SYMBOL(blk_queue_hardsect_size);
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/*
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* Returns the minimum that is _not_ zero, unless both are zero.
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*/
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#define min_not_zero(l, r) (l == 0) ? r : ((r == 0) ? l : min(l, r))
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/**
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* blk_queue_stack_limits - inherit underlying queue limits for stacked drivers
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* @t: the stacking driver (top)
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* @b: the underlying device (bottom)
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**/
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void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
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{
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/* zero is "infinity" */
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t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
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t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
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t->max_phys_segments = min(t->max_phys_segments, b->max_phys_segments);
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t->max_hw_segments = min(t->max_hw_segments, b->max_hw_segments);
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t->max_segment_size = min(t->max_segment_size, b->max_segment_size);
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t->hardsect_size = max(t->hardsect_size, b->hardsect_size);
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if (!t->queue_lock)
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WARN_ON_ONCE(1);
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else if (!test_bit(QUEUE_FLAG_CLUSTER, &b->queue_flags)) {
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unsigned long flags;
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spin_lock_irqsave(t->queue_lock, flags);
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queue_flag_clear(QUEUE_FLAG_CLUSTER, t);
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spin_unlock_irqrestore(t->queue_lock, flags);
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}
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}
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EXPORT_SYMBOL(blk_queue_stack_limits);
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/**
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* blk_queue_dma_pad - set pad mask
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* @q: the request queue for the device
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* @mask: pad mask
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*
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* Set dma pad mask.
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*
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* Appending pad buffer to a request modifies the last entry of a
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* scatter list such that it includes the pad buffer.
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**/
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void blk_queue_dma_pad(struct request_queue *q, unsigned int mask)
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{
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q->dma_pad_mask = mask;
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}
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EXPORT_SYMBOL(blk_queue_dma_pad);
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/**
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* blk_queue_update_dma_pad - update pad mask
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* @q: the request queue for the device
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* @mask: pad mask
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*
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* Update dma pad mask.
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*
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* Appending pad buffer to a request modifies the last entry of a
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* scatter list such that it includes the pad buffer.
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**/
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void blk_queue_update_dma_pad(struct request_queue *q, unsigned int mask)
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{
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if (mask > q->dma_pad_mask)
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q->dma_pad_mask = mask;
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}
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EXPORT_SYMBOL(blk_queue_update_dma_pad);
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/**
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* blk_queue_dma_drain - Set up a drain buffer for excess dma.
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* @q: the request queue for the device
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* @dma_drain_needed: fn which returns non-zero if drain is necessary
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* @buf: physically contiguous buffer
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* @size: size of the buffer in bytes
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*
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* Some devices have excess DMA problems and can't simply discard (or
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* zero fill) the unwanted piece of the transfer. They have to have a
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* real area of memory to transfer it into. The use case for this is
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* ATAPI devices in DMA mode. If the packet command causes a transfer
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* bigger than the transfer size some HBAs will lock up if there
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* aren't DMA elements to contain the excess transfer. What this API
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* does is adjust the queue so that the buf is always appended
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* silently to the scatterlist.
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*
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* Note: This routine adjusts max_hw_segments to make room for
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* appending the drain buffer. If you call
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* blk_queue_max_hw_segments() or blk_queue_max_phys_segments() after
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* calling this routine, you must set the limit to one fewer than your
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* device can support otherwise there won't be room for the drain
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* buffer.
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*/
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int blk_queue_dma_drain(struct request_queue *q,
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dma_drain_needed_fn *dma_drain_needed,
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void *buf, unsigned int size)
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{
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if (q->max_hw_segments < 2 || q->max_phys_segments < 2)
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return -EINVAL;
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/* make room for appending the drain */
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--q->max_hw_segments;
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--q->max_phys_segments;
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q->dma_drain_needed = dma_drain_needed;
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q->dma_drain_buffer = buf;
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q->dma_drain_size = size;
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return 0;
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}
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EXPORT_SYMBOL_GPL(blk_queue_dma_drain);
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/**
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* blk_queue_segment_boundary - set boundary rules for segment merging
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* @q: the request queue for the device
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* @mask: the memory boundary mask
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**/
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void blk_queue_segment_boundary(struct request_queue *q, unsigned long mask)
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{
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if (mask < PAGE_CACHE_SIZE - 1) {
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mask = PAGE_CACHE_SIZE - 1;
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printk(KERN_INFO "%s: set to minimum %lx\n",
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__func__, mask);
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}
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q->seg_boundary_mask = mask;
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}
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EXPORT_SYMBOL(blk_queue_segment_boundary);
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/**
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* blk_queue_dma_alignment - set dma length and memory alignment
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* @q: the request queue for the device
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* @mask: alignment mask
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*
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* description:
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* set required memory and length alignment for direct dma transactions.
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* this is used when buiding direct io requests for the queue.
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*
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**/
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void blk_queue_dma_alignment(struct request_queue *q, int mask)
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{
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q->dma_alignment = mask;
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}
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EXPORT_SYMBOL(blk_queue_dma_alignment);
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/**
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* blk_queue_update_dma_alignment - update dma length and memory alignment
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* @q: the request queue for the device
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* @mask: alignment mask
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*
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* description:
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* update required memory and length alignment for direct dma transactions.
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* If the requested alignment is larger than the current alignment, then
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* the current queue alignment is updated to the new value, otherwise it
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* is left alone. The design of this is to allow multiple objects
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|
* (driver, device, transport etc) to set their respective
|
|
* alignments without having them interfere.
|
|
*
|
|
**/
|
|
void blk_queue_update_dma_alignment(struct request_queue *q, int mask)
|
|
{
|
|
BUG_ON(mask > PAGE_SIZE);
|
|
|
|
if (mask > q->dma_alignment)
|
|
q->dma_alignment = mask;
|
|
}
|
|
EXPORT_SYMBOL(blk_queue_update_dma_alignment);
|
|
|
|
static int __init blk_settings_init(void)
|
|
{
|
|
blk_max_low_pfn = max_low_pfn - 1;
|
|
blk_max_pfn = max_pfn - 1;
|
|
return 0;
|
|
}
|
|
subsys_initcall(blk_settings_init);
|