From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: riel@redhat.com, linux-kernel@vger.kernel.org,
fweisbec@gmail.com, mingo@kernel.org, luto@amacapital.net,
clark@redhat.com
Subject: Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals
Date: Mon, 1 Feb 2016 10:22:23 +0100 [thread overview]
Message-ID: <20160201092223.GL6357@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.DEB.2.11.1602010933240.25254@nanos>
On Mon, Feb 01, 2016 at 09:37:00AM +0100, Thomas Gleixner wrote:
> On Sun, 31 Jan 2016, riel@redhat.com wrote:
> > @@ -93,9 +93,9 @@ 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 / (1000 * KB);
> > + stats->virtmem = p->acct_vm_mem1 * PAGE_SIZE / (1000 * KB);
>
> You replace "/ (1024 * 1024)" by "/ (1000 * 1024). So that's introducing a non
> power of 2 division instead of removing one and wont compile on systems which
> do not have a 64/32 division in hardware.
Yep, so that needs to be fixed to use do_div(). But the reason for this
is that this is the consumer side of these stats and therefore rarely
executed.
This patch effectively moves a div out of the fast path into the slow
path.
next prev parent reply other threads:[~2016-02-01 9:22 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-01 2:12 [PATCH 0/4 v3] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-01 2:12 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-02-01 4:46 ` kbuild test robot
2016-02-01 8:37 ` Thomas Gleixner
2016-02-01 9:22 ` Peter Zijlstra [this message]
2016-02-01 9:31 ` Thomas Gleixner
2016-02-01 13:44 ` Rik van Riel
2016-02-01 13:51 ` Peter Zijlstra
2016-02-01 2:12 ` [PATCH 2/4] acct,time: change indentation in __acct_update_integrals riel
2016-02-01 2:12 ` [PATCH 3/4] time,acct: drop irq save & restore from __acct_update_integrals riel
2016-02-01 9:28 ` Peter Zijlstra
2016-02-01 19:22 ` Rik van Riel
2016-02-01 2:12 ` [PATCH 4/4] sched,time: only call account_{user,sys,guest,idle}_time once a jiffy riel
2016-02-01 9:29 ` Peter Zijlstra
2016-02-01 19:23 ` Rik van Riel
2016-02-01 7:41 ` [PATCH] perf tooling: Add 'perf bench syscall' benchmark Ingo Molnar
2016-02-01 7:48 ` [PATCH] perf tooling: Simplify 'perf bench syscall' Ingo Molnar
2016-02-01 15:41 ` [PATCH] perf tooling: Add 'perf bench syscall' benchmark Andy Lutomirski
2016-02-03 10:22 ` Ingo Molnar
2016-06-20 18:00 ` [PATCH] perf: add 'perf bench syscall' Josh Poimboeuf
2016-06-20 19:16 ` Andy Lutomirski
2016-06-21 14:55 ` Josh Poimboeuf
2016-06-21 16:31 ` Andy Lutomirski
-- strict thread matches above, loose matches on Subject: below --
2016-02-11 1:08 [PATCH 0/4 v6] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-11 1:08 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-02-02 17:19 [PATCH 0/4 v5] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-02 17:19 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-02-01 19:21 [PATCH 0/4 v4] sched,time: reduce nohz_full syscall overhead 40% riel
2016-02-01 19:21 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-01-30 3:36 [PATCH 0/2] sched,time: reduce nohz_full syscall overhead 40% riel
2016-01-30 3:36 ` [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel
2016-01-30 4:56 ` kbuild test robot
2016-01-30 14:44 ` Frederic Weisbecker
2016-01-30 17:53 ` Rik van Riel
2016-02-01 11:30 ` Peter Zijlstra
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