From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753264AbcBATVO (ORCPT ); Mon, 1 Feb 2016 14:21:14 -0500 Received: from shelob.surriel.com ([74.92.59.67]:54518 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752407AbcBATVL (ORCPT ); Mon, 1 Feb 2016 14:21:11 -0500 From: riel@redhat.com To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, peterz@infradead.org, fweisbec@gmail.com, clark@redhat.com, luto@amacapital.net, mingo@kernel.org Subject: [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals Date: Mon, 1 Feb 2016 14:21:03 -0500 Message-Id: <1454354466-31309-2-git-send-email-riel@redhat.com> X-Mailer: git-send-email 2.5.0 In-Reply-To: <1454354466-31309-1-git-send-email-riel@redhat.com> References: <1454354466-31309-1-git-send-email-riel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel 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 --- 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); } -- 2.5.0