From: riel@redhat.com
To: linux-kernel@vger.kernel.org
Cc: fweisbec@gmail.com, tglx@linutronix.de, mingo@kernel.org,
luto@amacapital.net, peterz@infradead.org, clark@redhat.com,
eric.dumazet@gmail.com
Subject: [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals
Date: Tue, 2 Feb 2016 12:19:45 -0500 [thread overview]
Message-ID: <1454433586-3234-4-git-send-email-riel@redhat.com> (raw)
In-Reply-To: <1454433586-3234-1-git-send-email-riel@redhat.com>
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
next prev parent reply other threads:[~2016-02-02 17:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-02 17:19 [PATCH 0/4 v5] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-02 17:19 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-02-02 17:19 ` [PATCH 2/4] acct,time: change indentation in __acct_update_integrals riel
2016-02-02 17:19 ` riel [this message]
2016-02-02 17:19 ` [PATCH 4/4] sched,time: only call account_{user,sys,guest,idle}_time once a jiffy riel
2016-02-09 17:11 ` Frederic Weisbecker
2016-02-09 18:13 ` Rik van Riel
2016-02-09 21:20 ` Rik van Riel
2016-02-08 21:07 ` [PATCH 0/4 v5] sched,time: reduce nohz_full syscall overhead 40% Rik van Riel
2016-02-09 2:13 ` Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2016-02-11 1:08 [PATCH 0/4 v6] " riel
2016-02-11 1:08 ` [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals riel
2016-02-01 19:21 [PATCH 0/4 v4] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-01 19:21 ` [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals riel
2016-02-01 2:12 [PATCH 0/4 v3] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-01 2:12 ` [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals riel
2016-02-01 9:28 ` Peter Zijlstra
2016-02-01 19:22 ` Rik van Riel
2016-01-30 3:36 [PATCH 0/2] sched,time: reduce nohz_full syscall overhead 40% riel
2016-01-30 3:36 ` [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals riel
2016-01-30 16:24 ` Frederic Weisbecker
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