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rcu: Add event-tracing for RCU callback invocation 

There was recently some controversy about the overhead of invoking RCU
callbacks.  Add TRACE_EVENT()s to obtain fine-grained timings for the
start and stop of a batch of callbacks and also for each callback invoked.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2011-06-17 15:53:19 -07:00 committed by Paul E. McKenney
parent 9d68197c05
commit 29c00b4a1d
6 changed files with 219 additions and 54 deletions
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50
include/linux/rcupdate.h
View File

@ -794,44 +794,6 @@ static inline notrace void rcu_read_unlock_sched_notrace(void)
#define RCU_INIT_POINTER(p, v) \
p = (typeof(*v) __force __rcu *)(v)
/*
* debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
* by call_rcu() and rcu callback execution, and are therefore not part of the
* RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
*/
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
# define STATE_RCU_HEAD_READY 0
# define STATE_RCU_HEAD_QUEUED 1
extern struct debug_obj_descr rcuhead_debug_descr;
static inline void debug_rcu_head_queue(struct rcu_head *head)
{
WARN_ON_ONCE((unsigned long)head & 0x3);
debug_object_activate(head, &rcuhead_debug_descr);
debug_object_active_state(head, &rcuhead_debug_descr,
STATE_RCU_HEAD_READY,
STATE_RCU_HEAD_QUEUED);
}
static inline void debug_rcu_head_unqueue(struct rcu_head *head)
{
debug_object_active_state(head, &rcuhead_debug_descr,
STATE_RCU_HEAD_QUEUED,
STATE_RCU_HEAD_READY);
debug_object_deactivate(head, &rcuhead_debug_descr);
}
#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
static inline void debug_rcu_head_queue(struct rcu_head *head)
{
}
static inline void debug_rcu_head_unqueue(struct rcu_head *head)
{
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
{
return offset < 4096;
@ -850,18 +812,6 @@ void __kfree_rcu(struct rcu_head *head, unsigned long offset)
call_rcu(head, (rcu_callback)offset);
}
extern void kfree(const void *);
static inline void __rcu_reclaim(struct rcu_head *head)
{
unsigned long offset = (unsigned long)head->func;
if (__is_kfree_rcu_offset(offset))
kfree((void *)head - offset);
else
head->func(head);
}
/**
* kfree_rcu() - kfree an object after a grace period.
* @ptr: pointer to kfree

98
include/trace/events/rcu.h Normal file
View File

@ -0,0 +1,98 @@
#undef TRACE_SYSTEM
#define TRACE_SYSTEM rcu
#if !defined(_TRACE_RCU_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_RCU_H
#include <linux/tracepoint.h>
/*
* Tracepoint for calling rcu_do_batch, performed to start callback invocation:
*/
TRACE_EVENT(rcu_batch_start,
TP_PROTO(long callbacks_ready, int blimit),
TP_ARGS(callbacks_ready, blimit),
TP_STRUCT__entry(
__field( long, callbacks_ready )
__field( int, blimit )
),
TP_fast_assign(
__entry->callbacks_ready = callbacks_ready;
__entry->blimit = blimit;
),
TP_printk("CBs=%ld bl=%d", __entry->callbacks_ready, __entry->blimit)
);
/*
* Tracepoint for the invocation of a single RCU callback
*/
TRACE_EVENT(rcu_invoke_callback,
TP_PROTO(struct rcu_head *rhp),
TP_ARGS(rhp),
TP_STRUCT__entry(
__field( void *, rhp )
__field( void *, func )
),
TP_fast_assign(
__entry->rhp = rhp;
__entry->func = rhp->func;
),
TP_printk("rhp=%p func=%pf", __entry->rhp, __entry->func)
);
/*
* Tracepoint for the invocation of a single RCU kfree callback
*/
TRACE_EVENT(rcu_invoke_kfree_callback,
TP_PROTO(struct rcu_head *rhp, unsigned long offset),
TP_ARGS(rhp, offset),
TP_STRUCT__entry(
__field(void *, rhp )
__field(unsigned long, offset )
),
TP_fast_assign(
__entry->rhp = rhp;
__entry->offset = offset;
),
TP_printk("rhp=%p func=%ld", __entry->rhp, __entry->offset)
);
/*
* Tracepoint for leaving rcu_do_batch, performed after callback invocation:
*/
TRACE_EVENT(rcu_batch_end,
TP_PROTO(int callbacks_invoked),
TP_ARGS(callbacks_invoked),
TP_STRUCT__entry(
__field( int, callbacks_invoked )
),
TP_fast_assign(
__entry->callbacks_invoked = callbacks_invoked;
),
TP_printk("CBs-invoked=%d", __entry->callbacks_invoked)
);
#endif /* _TRACE_RCU_H */
/* This part must be outside protection */
#include <trace/define_trace.h>

79
kernel/rcu.h Normal file
View File

@ -0,0 +1,79 @@
/*
* Read-Copy Update definitions shared among RCU implementations.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright IBM Corporation, 2011
*
* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*/
#ifndef __LINUX_RCU_H
#define __LINUX_RCU_H
/*
* debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
* by call_rcu() and rcu callback execution, and are therefore not part of the
* RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
*/
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
# define STATE_RCU_HEAD_READY 0
# define STATE_RCU_HEAD_QUEUED 1
extern struct debug_obj_descr rcuhead_debug_descr;
static inline void debug_rcu_head_queue(struct rcu_head *head)
{
WARN_ON_ONCE((unsigned long)head & 0x3);
debug_object_activate(head, &rcuhead_debug_descr);
debug_object_active_state(head, &rcuhead_debug_descr,
STATE_RCU_HEAD_READY,
STATE_RCU_HEAD_QUEUED);
}
static inline void debug_rcu_head_unqueue(struct rcu_head *head)
{
debug_object_active_state(head, &rcuhead_debug_descr,
STATE_RCU_HEAD_QUEUED,
STATE_RCU_HEAD_READY);
debug_object_deactivate(head, &rcuhead_debug_descr);
}
#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
static inline void debug_rcu_head_queue(struct rcu_head *head)
{
}
static inline void debug_rcu_head_unqueue(struct rcu_head *head)
{
}
#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
extern void kfree(const void *);
static inline void __rcu_reclaim(struct rcu_head *head)
{
unsigned long offset = (unsigned long)head->func;
if (__is_kfree_rcu_offset(offset)) {
trace_rcu_invoke_kfree_callback(head, offset);
kfree((void *)head - offset);
} else {
trace_rcu_invoke_callback(head);
head->func(head);
}
}
#endif /* __LINUX_RCU_H */

5
kernel/rcupdate.c
View File

@ -46,6 +46,11 @@
#include <linux/module.h>
#include <linux/hardirq.h>
#define CREATE_TRACE_POINTS
#include <trace/events/rcu.h>
#include "rcu.h"
#ifdef CONFIG_DEBUG_LOCK_ALLOC
static struct lock_class_key rcu_lock_key;
struct lockdep_map rcu_lock_map =

26
kernel/rcutiny.c
View File

@ -37,6 +37,25 @@
#include <linux/cpu.h>
#include <linux/prefetch.h>
#ifdef CONFIG_RCU_TRACE
#include <trace/events/rcu.h>
#else /* #ifdef CONFIG_RCU_TRACE */
/* No by-default tracing in TINY_RCU: Keep TINY_RCU tiny! */
static void trace_rcu_invoke_kfree_callback(struct rcu_head *rhp,
unsigned long offset)
{
}
static void trace_rcu_invoke_callback(struct rcu_head *head)
{
}
#endif /* #else #ifdef CONFIG_RCU_TRACE */
#include "rcu.h"
/* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
static struct task_struct *rcu_kthread_task;
static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
@ -161,11 +180,15 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
RCU_TRACE(int cb_count = 0);
/* If no RCU callbacks ready to invoke, just return. */
if (&rcp->rcucblist == rcp->donetail)
if (&rcp->rcucblist == rcp->donetail) {
RCU_TRACE(trace_rcu_batch_start(0, -1));
RCU_TRACE(trace_rcu_batch_end(0));
return;
}
/* Move the ready-to-invoke callbacks to a local list. */
local_irq_save(flags);
RCU_TRACE(trace_rcu_batch_start(0, -1));
list = rcp->rcucblist;
rcp->rcucblist = *rcp->donetail;
*rcp->donetail = NULL;
@ -187,6 +210,7 @@ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
RCU_TRACE(cb_count++);
}
RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
RCU_TRACE(trace_rcu_batch_end(cb_count));
}
/*

15
kernel/rcutree.c
View File

@ -52,6 +52,9 @@
#include <linux/prefetch.h>
#include "rcutree.h"
#include <trace/events/rcu.h>
#include "rcu.h"
/* Data structures. */
@ -1190,17 +1193,22 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
{
unsigned long flags;
struct rcu_head *next, *list, **tail;
int count;
int bl, count;
/* If no callbacks are ready, just return.*/
if (!cpu_has_callbacks_ready_to_invoke(rdp))
if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
trace_rcu_batch_start(0, 0);
trace_rcu_batch_end(0);
return;
}
/*
* Extract the list of ready callbacks, disabling to prevent
* races with call_rcu() from interrupt handlers.
*/
local_irq_save(flags);
bl = rdp->blimit;
trace_rcu_batch_start(rdp->qlen, bl);
list = rdp->nxtlist;
rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
*rdp->nxttail[RCU_DONE_TAIL] = NULL;
@ -1218,11 +1226,12 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
debug_rcu_head_unqueue(list);
__rcu_reclaim(list);
list = next;
if (++count >= rdp->blimit)
if (++count >= bl)
break;
}
local_irq_save(flags);
trace_rcu_batch_end(count);
/* Update count, and requeue any remaining callbacks. */
rdp->qlen -= count;