Commit-ID: 9344c92c2e72e495f695caef8364b3dd73af0eab Gitweb: http://git.kernel.org/tip/9344c92c2e72e495f695caef8364b3dd73af0eab Author: Rik van Riel <r...@redhat.com> AuthorDate: Wed, 10 Feb 2016 20:08:26 -0500 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 29 Feb 2016 09:53:09 +0100
time, acct: Drop irq save & restore from __acct_update_integrals() 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 <pet...@infradead.org> Signed-off-by: Rik van Riel <r...@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Reviewed-by: Thomas Gleixner <t...@linutronix.de> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mike Galbraith <efa...@gmx.de> Cc: cl...@redhat.com Cc: eric.duma...@gmail.com Cc: fweis...@gmail.com Cc: l...@amacapital.net Link: http://lkml.kernel.org/r/1455152907-18495-4-git-send-email-r...@redhat.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- kernel/tsacct.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/tsacct.c b/kernel/tsacct.c index d12e815..f8e26ab 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 @@ out: 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); } /**
