[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <1454106180-20918-2-git-send-email-riel@redhat.com>
Date: Fri, 29 Jan 2016 17:22:59 -0500
From: riel@...hat.com
To: linux-kernel@...r.kernel.org
Cc: tglx@...utronix.de, mingo@...nel.org, peterz@...radead.org,
luto@...capital.net, fweisbec@...il.com
Subject: [PATCH 1/2] sched,time: remove pointless divides from __acct_update_integrals
From: Rik van Riel <riel@...hat.com>
When running a microbenchmark calling an invalid syscall number
in a loop, on a nohz_full CPU, we spend a full 9% of our CPU
time in __acct_update_integrals.
This function converts cputime_t to jiffies, to a timeval, only to
convert the timeval back to microseconds before discarding it.
This patch leaves __acct_update_integrals functionally equivalent,
but speeds things up by about 11%, with 10 million calls to an
invalid syscall number dropping from 3.7 to 3.3 seconds.
Signed-off-by: Rik van Riel <riel@...hat.com>
---
kernel/tsacct.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 975cb49e32bf..afb5cf8ecc5f 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -125,22 +125,22 @@ static void __acct_update_integrals(struct task_struct *tsk,
{
if (likely(tsk->mm)) {
cputime_t time, dtime;
- struct timeval value;
unsigned long flags;
- u64 delta;
+ u64 delta, usecs;
local_irq_save(flags);
time = stime + utime;
dtime = time - tsk->acct_timexpd;
- jiffies_to_timeval(cputime_to_jiffies(dtime), &value);
- delta = value.tv_sec;
- delta = delta * USEC_PER_SEC + value.tv_usec;
+ delta = cputime_to_jiffies(dtime);
if (delta == 0)
goto out;
+
+ usecs = jiffies_to_usecs(delta);
+
tsk->acct_timexpd = time;
- tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
- tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;
+ tsk->acct_rss_mem1 += usecs * get_mm_rss(tsk->mm);
+ tsk->acct_vm_mem1 += usecs * tsk->mm->total_vm;
out:
local_irq_restore(flags);
}
--
2.5.0
Powered by blists - more mailing lists