From 382c2fe994321d503647ce8ee329b9420dc7c1f9 Mon Sep 17 00:00:00 2001 From: Rik van Riel Date: Wed, 10 Feb 2016 20:08:24 -0500 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Thomas Gleixner Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: clark@redhat.com Cc: eric.dumazet@gmail.com Cc: fweisbec@gmail.com Cc: luto@amacapital.net Link: http://lkml.kernel.org/r/1455152907-18495-2-git-send-email-riel@redhat.com Signed-off-by: Ingo Molnar --- kernel/tsacct.c | 26 ++++++++++++++++---------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/kernel/tsacct.c b/kernel/tsacct.c index 975cb49e32bf..460ee2bbfef3 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); } -- 2.20.1