Messages in this thread | | | Subject | Re: scheduler vs hardware? (was Re: another i7 (linux) bug?) | From | Mike Galbraith <> | Date | Fri, 22 Jan 2010 10:10:57 +0100 |
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On Fri, 2010-01-22 at 09:51 +0100, Peter Zijlstra wrote: > On Fri, 2010-01-22 at 08:19 +0100, Mike Galbraith wrote: > > > if I run a cpu intensive process with the lowest priority (19 > > > from man nice) I obtain much better performance that with the > > > highest priority available (-20 from man nice). > > > > > > For example the same file is processed by lame in 8.7 seconds > > > at the lowest priority, and in 12 seconds at the highest > > > priority. Before posting a bug I wold like to understand if > > > this is a problem related to the i7 mobile (my processor is a > > > i7 Q720). > > > > > > As far as I tested on the same laptop series (dell studio 15), > > > with the same kernel this problem does not exists. > > > > So you only see this on the i7. That's odd. Can you try 33-rc5? > > > > Posting a reliable reproducer would be nice. It'd also be nice to see > > what all is running when you see this, and where. > > Using a sample from: http://lame.sourceforge.net/quality.php > > My laptop does: > > > # time nice -n 19 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m3.273s > user 0m3.217s > sys 0m0.022s > > > # time nice -n 0 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m1.121s > user 0m1.102s > sys 0m0.013s > > > # time nice -n -20 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m1.112s > user 0m1.093s > sys 0m0.018s > > > > On a Nehalem class server machine it does: > > > # time nice -n 19 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m0.932s > user 0m0.917s > sys 0m0.005s > > > # time nice -n 0 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m0.927s > user 0m0.922s > sys 0m0.003s > > > # time nice -n -20 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
> real 0m0.919s > user 0m0.914s > sys 0m0.005s
Weird. Here there is zip squat difference, as expected with 1 thread.
time nice -n 19 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
real 0m0.912s user 0m0.908s sys 0m0.000s
time nice -n 0 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
real 0m0.912s user 0m0.904s sys 0m0.004s
time nice -n -20 lame -b 256 -V0 -h youcantdothat.wav - > /dev/null
real 0m0.912s user 0m0.904s sys 0m0.004s
(bah, who needs a nehalem;)
-Mike
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