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aoe: use high-resolution RTTs with fallback to low-res 

These changes improve the accuracy of the decision about whether it's time
to retransmit an AoE command by using the microsecond-resolution
gettimeofday instead of jiffies.

Because the system time can jump suddenly, the decision reverts to using
jiffies if the high-resolution time difference is relatively large.
Otherwise the AoE targets could be considered failed inappropriately.

Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ed Cashin 2012-12-17 16:03:49 -08:00 committed by Linus Torvalds
parent 0d555ecfa4
commit 5f0c9c48e7
2 changed files with 55 additions and 11 deletions
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9
drivers/block/aoe/aoe.h
View File

@ -88,8 +88,7 @@ enum {
TIMERTICK = HZ / 10,
RTTSCALE = 8,
RTTDSCALE = 3,
MAXTIMER = HZ << 1,
RTTAVG_INIT = HZ / 4 << RTTSCALE,
RTTAVG_INIT = USEC_PER_SEC / 4 << RTTSCALE,
RTTDEV_INIT = RTTAVG_INIT / 4,
};
@ -106,6 +105,8 @@ struct buf {
struct frame {
struct list_head head;
u32 tag;
struct timeval sent; /* high-res time packet was sent */
u32 sent_jiffs; /* low-res jiffies-based sent time */
ulong waited;
struct aoetgt *t; /* parent target I belong to */
sector_t lba;
@ -143,11 +144,11 @@ struct aoedev {
struct aoedev *next;
ulong sysminor;
ulong aoemajor;
u32 rttavg; /* scaled AoE round trip time average */
u32 rttdev; /* scaled round trip time mean deviation */
u16 aoeminor;
u16 flags;
u16 nopen; /* (bd_openers isn't available without sleeping) */
u16 rttavg; /* scaled AoE round trip time average */
u16 rttdev; /* scaled round trip time mean deviation */
u16 fw_ver; /* version of blade's firmware */
u16 lasttag; /* last tag sent */
u16 useme;

57
drivers/block/aoe/aoecmd.c
View File

@ -387,6 +387,8 @@ aoecmd_ata_rw(struct aoedev *d)
skb->dev = t->ifp->nd;
skb = skb_clone(skb, GFP_ATOMIC);
if (skb) {
do_gettimeofday(&f->sent);
f->sent_jiffs = (u32) jiffies;
__skb_queue_head_init(&queue);
__skb_queue_tail(&queue, skb);
aoenet_xmit(&queue);
@ -475,11 +477,45 @@ resend(struct aoedev *d, struct frame *f)
skb = skb_clone(skb, GFP_ATOMIC);
if (skb == NULL)
return;
do_gettimeofday(&f->sent);
f->sent_jiffs = (u32) jiffies;
__skb_queue_head_init(&queue);
__skb_queue_tail(&queue, skb);
aoenet_xmit(&queue);
}
static int
tsince_hr(struct frame *f)
{
struct timeval now;
int n;
do_gettimeofday(&now);
n = now.tv_usec - f->sent.tv_usec;
n += (now.tv_sec - f->sent.tv_sec) * USEC_PER_SEC;
if (n < 0)
n = -n;
/* For relatively long periods, use jiffies to avoid
* discrepancies caused by updates to the system time.
*
* On system with HZ of 1000, 32-bits is over 49 days
* worth of jiffies, or over 71 minutes worth of usecs.
*
* Jiffies overflow is handled by subtraction of unsigned ints:
* (gdb) print (unsigned) 2 - (unsigned) 0xfffffffe
* $3 = 4
* (gdb)
*/
if (n > USEC_PER_SEC / 4) {
n = ((u32) jiffies) - f->sent_jiffs;
n *= USEC_PER_SEC / HZ;
}
return n;
}
static int
tsince(u32 tag)
{
@ -489,7 +525,7 @@ tsince(u32 tag)
n -= tag & 0xffff;
if (n < 0)
n += 1<<16;
return n;
return jiffies_to_usecs(n + 1);
}
static struct aoeif *
@ -552,6 +588,7 @@ sthtith(struct aoedev *d)
nf->bv = f->bv;
nf->bv_off = f->bv_off;
nf->waited = 0;
nf->sent_jiffs = f->sent_jiffs;
f->skb = skb;
aoe_freetframe(f);
ht->nout--;
@ -621,7 +658,7 @@ rexmit_timer(ulong vp)
head = &d->factive[i];
list_for_each_safe(pos, nx, head) {
f = list_entry(pos, struct frame, head);
if (tsince(f->tag) < timeout)
if (tsince_hr(f) < timeout)
break; /* end of expired frames */
/* move to flist for later processing */
list_move_tail(pos, &flist);
@ -632,8 +669,8 @@ rexmit_timer(ulong vp)
while (!list_empty(&flist)) {
pos = flist.next;
f = list_entry(pos, struct frame, head);
n = f->waited += tsince(f->tag);
n /= HZ;
n = f->waited += tsince_hr(f);
n /= USEC_PER_SEC;
if (n > aoe_deadsecs) {
/* Waited too long. Device failure.
* Hang all frames on first hash bucket for downdev
@ -1193,12 +1230,12 @@ aoecmd_ata_rsp(struct sk_buff *skb)
n = be32_to_cpu(get_unaligned(&h->tag));
f = getframe(d, n);
if (f) {
calc_rttavg(d, f->t, tsince(n));
calc_rttavg(d, f->t, tsince_hr(f));
f->t->nout--;
} else {
f = getframe_deferred(d, n);
if (f) {
calc_rttavg(d, NULL, tsince(n));
calc_rttavg(d, NULL, tsince_hr(f));
} else {
calc_rttavg(d, NULL, tsince(n));
spin_unlock_irqrestore(&d->lock, flags);
@ -1276,7 +1313,13 @@ aoecmd_ata_id(struct aoedev *d)
d->rttdev = RTTDEV_INIT;
d->timer.function = rexmit_timer;
return skb_clone(skb, GFP_ATOMIC);
skb = skb_clone(skb, GFP_ATOMIC);
if (skb) {
do_gettimeofday(&f->sent);
f->sent_jiffs = (u32) jiffies;
}
return skb;
}
static struct aoetgt *