svn commit: r281103 - head/sys/amd64/amd64

[John-Mark Gurney]

Kurt Lidl wrote this message on Wed, May 27, 2015 at 09:53 -0400:
> On 4/6/15 1:42 AM, Bruce Evans wrote:
> > On Mon, 6 Apr 2015, Eitan Adler wrote:
> >
> >> + a few people interested in the diff
> >>
> >> On 5 April 2015 at 02:55, Bruce Evans <brde at optusnet.com.au> wrote:
> >>> On Sun, 5 Apr 2015, Eitan Adler wrote:
> >>
> >> I did not confirm the performance impact, but the submitter and others
> >> indicated they saw a difference.
> >>
> >> Do you have specific data that shows that there was an improvement?
> >
> > Only micro-benchmark output that indicates little difference.  This
> > is probably very MD (depending on write combining hardware), so you
> > might only see a difference on some systems.
> >
> > I also have micro-benchmark output for network packets/second that
> > shows 10% differences for the change of adding 1 byte of padding
> > in code that is never executed.  This seems to be due to different
> > cache misses.  To eliminate differences from this (except ones
> > caused by actually running different code), create a reference
> > version by padding the functions or data to be changed so that
> > the change doesn't affect the address of anything except the
> > internals of the changed parts.
> >
> > I might try a makeworld run to see if changing the non-temporal
> > accesses in pagecopy and pagezero to cached.
> 
> 
> I ran a few (total of 12) buildworld runs after this discussion.
> I finally got around to posting the results to the original bug.
> 
> The data is here:
> 
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=199151#c3

If you run ministat on the real results, there won't be a difference
w/ 95% confidence...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."