Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals

From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals
Date	2016-02-01 10:40 +0100
Message-ID	<qXj7I-Bb-5@gated-at.bofh.it> (permalink)
References	<qXcfT-45K-3@gated-at.bofh.it> <qXcfU-45K-9@gated-at.bofh.it> <qXibE-8pb-7@gated-at.bofh.it> <qXiY1-wH-1@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Mon, 1 Feb 2016, Peter Zijlstra wrote:

> 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.

Yeah, noticed after hitting Send :)

Thread

[PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals riel@redhat.com - 2016-02-01 03:20 +0100
  Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals kbuild test robot <lkp@intel.com> - 2016-02-01 05:50 +0100
  Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals Thomas Gleixner <tglx@linutronix.de> - 2016-02-01 09:40 +0100
    Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals Peter Zijlstra <peterz@infradead.org> - 2016-02-01 10:30 +0100
      Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals Thomas Gleixner <tglx@linutronix.de> - 2016-02-01 10:40 +0100
      Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals Rik van Riel <riel@redhat.com> - 2016-02-01 14:50 +0100
        Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from  __acct_update_integrals Peter Zijlstra <peterz@infradead.org> - 2016-02-01 15:00 +0100

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