From: Rik van Riel <r...@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.
Suggested-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Rik van Riel <r...@redhat.com>
---
kernel/tsacct.c | 6 +-----
1 file changed, 1 insertion(+), 5 deletions(-)
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 9c23584c76c4..31fb6c9746d4 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -124,20 +124,18 @@ 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;
/*
@@ -147,8 +145,6 @@ 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);
}
/**
--
2.5.0
