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 <peterz@infradead.org> Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: clark@redhat.com Cc: eric.dumazet@gmail.com Cc: fweisbec@gmail.com Cc: luto@amacapital.net Link: http://lkml.kernel.org/r/1455152907-18495-4-git-send-email-riel@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -126,20 +126,18 @@ static void __acct_update_integrals(struct task_struct *tsk,
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cputime_t utime, cputime_t stime)
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{
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cputime_t time, dtime;
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unsigned long flags;
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u64 delta;
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if (!likely(tsk->mm))
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return;
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local_irq_save(flags);
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time = stime + utime;
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dtime = time - tsk->acct_timexpd;
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/* Avoid division: cputime_t is often in nanoseconds already. */
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delta = cputime_to_nsecs(dtime);
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if (delta < TICK_NSEC)
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goto out;
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return;
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tsk->acct_timexpd = time;
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/*
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@ -149,8 +147,6 @@ static void __acct_update_integrals(struct task_struct *tsk,
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*/
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tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm) >> 10;
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tsk->acct_vm_mem1 += delta * tsk->mm->total_vm >> 10;
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out:
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local_irq_restore(flags);
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}
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/**
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@ -160,9 +156,12 @@ out:
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void acct_update_integrals(struct task_struct *tsk)
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{
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cputime_t utime, stime;
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unsigned long flags;
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local_irq_save(flags);
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task_cputime(tsk, &utime, &stime);
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__acct_update_integrals(tsk, utime, stime);
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local_irq_restore(flags);
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}
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/**
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