lkml.org 
[lkml]   [2015]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 02/10] perf/x86: Improve HT workaround GP counter constraint
On Fri, May 22, 2015 at 06:40:49AM -0700, Stephane Eranian wrote:
> On Fri, May 22, 2015 at 6:36 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Fri, May 22, 2015 at 06:29:47AM -0700, Stephane Eranian wrote:
> >> On Fri, May 22, 2015 at 6:25 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >> > On Fri, May 22, 2015 at 06:07:00AM -0700, Stephane Eranian wrote:
> >> >>
> >> >> One other thing I noticed is that the --n_excl needs to be protected by the
> >> >> excl_cntrs->lock in put_excl_constraints().
> >> >
> >> > Nah, its strictly per cpu.
> >>
> >> No. the excl_cntrs struct is pointed to by cpuc but it is shared between the
> >> sibling HT. Otherwise this would not work!
> >
> > n_excl is per cpuc, see the trickery with has_exclusive vs
> > exclusive_present on how I avoid the lock.
>
> Yes, but I believe you create a store forward penalty with this.
> You store 16bits and you load 32 bits on the same cache line.

The store and load are fairly well spaced -- the entire scheduling fast
path is in between.

And such a penalty is still cheap compared to locking, no?


\
 
 \ /
  Last update: 2015-05-22 16:21    [W:0.100 / U:1.060 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site