Re: less load less performance

[Alexey Fisher <bug-track@fisher-privat.net>]

Am Sonntag, den 31.10.2010, 20:18 +0100 schrieb Andreas Mohr:
> On Sun, Oct 31, 2010 at 06:40:26PM +0100, Alexey Fisher wrote:
> > Am Sonntag, den 31.10.2010, 17:01 +0000 schrieb Peter Clifton:
> > > On Sun, 2010-10-31 at 17:44 +0100, Alexey Fisher wrote:
> > > > Hallo all,
> > > > 
> > > > As i can understand if cpu do not get enough load it will work mostly in
> > > > C4 mode and graphic perfome slow too. I think there is some thing wrong
> > > > in this logic :)
> > > 
> > > Yes, a little messed up.. try running your test at low screen-res with
> > > this app running (once per core):
> > > 
> > > int main( int argc, char **argv )
> > > {
> > >   while (1);
> > > }
> > > 
> > > (gcc loop.c -o loop)
> > > 
> > > Do you get the high frames per second (non-full-screen) then?
> > 
> > Yes! it working smooth, with 60fps (i have only single core atom with HT
> > enabled)
> 
> Why painfully compile a custom c app to keep the CPU busy?
> 
> Boot with processor.max_cstate=1
> Much better performance? --> "BUG"!
> ("BUG" == "something should probably be done about these power management side
> effects")

for some reasons "processor.max_cstate=1" do not make any difference,
cpu still use C4. Interesting is maxcpus=1 do difference, C4 is used and
it perform good too. So what can it be? Some SMP scheduler problem, IRQ
balancing?
I know intel CPUs had some PM problem, if 1 core is disabled it consume
more power (may be no C4?). What talking against this theory:
1. if i start SMP and put one core off, this will make no difference
so maxcpus=1 and "echo 0 > /sys/devices/system/cpu/cpu1/online" is not
the same
2. i use Atom N280, there is only one core but HT is enabled.
-- 
Regards,
        Alexey