Commit-ID: 382c2fe994321d503647ce8ee329b9420dc7c1f9
Gitweb: http://git.kernel.org/tip/382c2fe994321d503647ce8ee329b9420dc7c1f9
Author: Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Wed, 10 Feb 2016 20:08:24 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Mon, 29 Feb 2016 09:53:08 +0100
sched, time: Remove non-power-of-two divides from __acct_update_integrals()
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 12%, with 10 million calls to an
invalid syscall number dropping from 3.7 to 3.25 seconds.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: clark@xxxxxxxxxx
Cc: eric.dumazet@xxxxxxxxx
Cc: fweisbec@xxxxxxxxx
Cc: luto@xxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1455152907-18495-2-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/tsacct.c | 26 ++++++++++++++++----------
1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 975cb49..460ee2b 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -93,9 +93,11 @@ void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
{
struct mm_struct *mm;
- /* convert pages-usec to Mbyte-usec */
- stats->coremem = p->acct_rss_mem1 * PAGE_SIZE / MB;
- stats->virtmem = p->acct_vm_mem1 * PAGE_SIZE / MB;
+ /* convert pages-nsec/1024 to Mbyte-usec, see __acct_update_integrals */
+ stats->coremem = p->acct_rss_mem1 * PAGE_SIZE;
+ do_div(stats->coremem, 1000 * KB);
+ stats->virtmem = p->acct_vm_mem1 * PAGE_SIZE;
+ do_div(stats->virtmem, 1000 * KB);
mm = get_task_mm(p);
if (mm) {
/* adjust to KB unit */
@@ -125,22 +127,26 @@ 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;
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;
+ /* Avoid division: cputime_t is often in nanoseconds already. */
+ delta = cputime_to_nsecs(dtime);
- if (delta == 0)
+ if (delta < TICK_NSEC)
goto out;
+
tsk->acct_timexpd = time;
- tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
- tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;
+ /*
+ * Divide by 1024 to avoid overflow, and to avoid division.
+ * The final unit reported to userspace is Mbyte-usecs,
+ * the rest of the math is done in xacct_add_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);
}
--
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