Messages in this thread | | | Date | Mon, 1 Feb 2016 10:22:23 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/4] sched,time: remove non-power-of-two divides from __acct_update_integrals |
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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.
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