Messages in this thread Patch in this message | | | From | riel@redhat ... | Subject | [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals | Date | Tue, 2 Feb 2016 12:19:45 -0500 |
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From: Rik van Riel <riel@redhat.com>
It looks like all the call paths that lead to __acct_update_integrals already have irqs disabled, and __acct_update_integrals does not need to disable irqs itself.
This is very convenient since about half the CPU time left in this function was spent in local_irq_save alone.
Performance of a microbenchmark that calls an invalid syscall ten million times in a row on a nohz_full CPU improves 21% vs. 4.5-rc1 with both the removal of divisions from __acct_update_integrals and this patch, with runtime dropping from 3.7 to 2.9 seconds.
With these patches applied, the highest remaining cpu user in the trace is native_sched_clock, which is addressed in the next patch.
For testing purposes I stuck a WARN_ON(!irqs_disabled()) test in __acct_update_integrals. It did not trigger.
Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Rik van Riel <riel@redhat.com> --- kernel/tsacct.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/kernel/tsacct.c b/kernel/tsacct.c index d12e815b7bcd..f8e26ab963ed 100644 --- a/kernel/tsacct.c +++ b/kernel/tsacct.c @@ -126,20 +126,18 @@ static void __acct_update_integrals(struct task_struct *tsk, cputime_t utime, cputime_t stime) { cputime_t time, dtime; - unsigned long flags; u64 delta; if (!likely(tsk->mm)) return; - local_irq_save(flags); time = stime + utime; dtime = time - tsk->acct_timexpd; /* Avoid division: cputime_t is often in nanoseconds already. */ delta = cputime_to_nsecs(dtime); if (delta < TICK_NSEC) - goto out; + return; tsk->acct_timexpd = time; /* @@ -149,8 +147,6 @@ static void __acct_update_integrals(struct task_struct *tsk, */ tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm) >> 10; tsk->acct_vm_mem1 += delta * tsk->mm->total_vm >> 10; -out: - local_irq_restore(flags); } /** @@ -160,9 +156,12 @@ static void __acct_update_integrals(struct task_struct *tsk, void acct_update_integrals(struct task_struct *tsk) { cputime_t utime, stime; + unsigned long flags; + local_irq_save(flags); task_cputime(tsk, &utime, &stime); __acct_update_integrals(tsk, utime, stime); + local_irq_restore(flags); } /** -- 2.5.0
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