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tracing, sched: LTTng instrumentation - scheduler

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Instrument the scheduler activity (sched_switch, migration, wakeups,
wait for a task, signal delivery) and process/thread
creation/destruction (fork, exit, kthread stop). Actually, kthread
creation is not instrumented in this patch because it is architecture
dependent. It allows to connect tracers such as ftrace which detects
scheduling latencies, good/bad scheduler decisions. Tools like LTTng can
export this scheduler information along with instrumentation of the rest
of the kernel activity to perform post-mortem analysis on the scheduler
activity.

About the performance impact of tracepoints (which is comparable to
markers), even without immediate values optimizations, tests done by
Hideo Aoki on ia64 show no regression. His test case was using hackbench
on a kernel where scheduler instrumentation (about 5 events in code
scheduler code) was added. See the "Tracepoints" patch header for
performance result detail.

Changelog :

- Change instrumentation location and parameter to match ftrace
  instrumentation, previously done with kernel markers.

[ [email protected]: conflict resolutions ]
Signed-off-by: Mathieu Desnoyers <[email protected]>
Acked-by: 'Peter Zijlstra' <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Mathieu Desnoyers 2008-07-18 12:16:17 -04:00 • committed by Ingo Molnar
commit 0a16b60758
6 changed files with 71 additions and 12 deletions
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17
kernel/sched.c
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@ -71,6 +71,7 @@
#include <linux/debugfs.h>
#include <linux/ctype.h>
#include <linux/ftrace.h>
#include <trace/sched.h>
#include <asm/tlb.h>
#include <asm/irq_regs.h>
@ -1936,6 +1937,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
* just go back and repeat.
*/
rq = task_rq_lock(p, &flags);
trace_sched_wait_task(rq, p);
running = task_running(rq, p);
on_rq = p->se.on_rq;
ncsw = 0;
@ -2297,9 +2299,7 @@ out_activate:
success = 1;
out_running:
trace_mark(kernel_sched_wakeup,
"pid %d state %ld ## rq %p task %p rq->curr %p",
p->pid, p->state, rq, p, rq->curr);
trace_sched_wakeup(rq, p);
check_preempt_curr(rq, p, sync);
p->state = TASK_RUNNING;
@ -2432,9 +2432,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
p->sched_class->task_new(rq, p);
inc_nr_running(rq);
}
trace_mark(kernel_sched_wakeup_new,
"pid %d state %ld ## rq %p task %p rq->curr %p",
p->pid, p->state, rq, p, rq->curr);
trace_sched_wakeup_new(rq, p);
check_preempt_curr(rq, p, 0);
#ifdef CONFIG_SMP
if (p->sched_class->task_wake_up)
@ -2607,11 +2605,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
struct mm_struct *mm, *oldmm;
prepare_task_switch(rq, prev, next);
trace_mark(kernel_sched_schedule,
"prev_pid %d next_pid %d prev_state %ld "
"## rq %p prev %p next %p",
prev->pid, next->pid, prev->state,
rq, prev, next);
trace_sched_switch(rq, prev, next);
mm = next->mm;
oldmm = prev->active_mm;
/*
@ -2851,6 +2845,7 @@ static void sched_migrate_task(struct task_struct *p, int dest_cpu)
|| unlikely(!cpu_active(dest_cpu)))
goto out;
trace_sched_migrate_task(rq, p, dest_cpu);
/* force the process onto the specified CPU */
if (migrate_task(p, dest_cpu, &req)) {
/* Need to wait for migration thread (might exit: take ref). */