lkml.org 
[lkml]   [2013]   [Oct]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86: Run checksumming in parallel accross multiple alu's
On Thu, Oct 31, 2013 at 11:22:00AM +0100, Ingo Molnar wrote:
>
> * Neil Horman <nhorman@tuxdriver.com> wrote:
>
> > > etc. For such short runtimes make sure the last column displays
> > > close to 100%, so that the PMU results become trustable.
> > >
> > > A nehalem+ PMU will allow 2-4 events to be measured in parallel,
> > > plus generics like 'cycles', 'instructions' can be added 'for free'
> > > because they get counted in a separate (fixed purpose) PMU register.
> > >
> > > The last colum tells you what percentage of the runtime that
> > > particular event was actually active. 100% (or empty last column)
> > > means it was active all the time.
> > >
> > > Thanks,
> > >
> > > Ingo
> > >
> >
> > Hmm,
> >
> > I ran this test:
> >
> > for i in `seq 0 1 3`
> > do
> > echo $i > /sys/module/csum_test/parameters/module_test_mode
> > taskset -c 0 perf stat --repeat 20 -C 0 -e L1-dcache-load-misses -e L1-dcache-prefetches -e cycles -e instructions -ddd ./test.sh
> > done
>
> You need to remove '-ddd' which is a shortcut for a ton of useful
> events, but here you want to use fewer events, to increase the
> precision of the measurement.
>
> Thanks,
>
> Ingo
>

Thank you ingo, that fixed it. I'm trying some other variants of the csum
algorithm that Doug and I discussed last night, but FWIW, the relative
performance of the 4 test cases (base/prefetch/parallel/both) remains unchanged.
I'm starting to feel like at this point, theres very little point in doing
parallel alu operations (unless we can find a way to break the dependency on the
carry flag, which is what I'm tinkering with now).
Neil



\
 
 \ /
  Last update: 2013-10-31 16:01    [W:0.121 / U:0.080 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site