linux-kernel - Re: [PATCH] cpufreq: fix conservative/ondemand behaviour with ignore_nice

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Date:	Wed, 11 Nov 2009 16:20:25 -0800
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	Alexander Miller <Miller@....uni-stuttgart.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH] cpufreq: fix conservative/ondemand behaviour with
 ignore_nice_load

On Wed, 2009-11-11 at 14:10 -0800, Alexander Miller wrote:
> On Tue, Nov 10, 2009, Pallipadi, Venkatesh wrote:
> > > Can you describe the "unresonable behavior" you are seeing. Is it
> > > with NO_HZ enabled or disabled?
> $ zgrep NO_HZ /proc/config.gz
> # CONFIG_NO_HZ is not set
> 
> When there are two cpu-intense processes, one with nice 19 and the other
> with nice 0, then the latter will use almost 100% cpu time, of course.
> But the cpu has been stuck at the lowest frequency without the patch.
> To be exact, it would change the freq sometimes, but return to the
> lowest freq within a fraction of a second.
> I would expect it to select a freq such that the non-nice processes
> take <80% or the highest freq (which it does with the patch).
> 
> > > I see there can be a problem with this code when NO_HZ is disabled.
> > > But, the patch below is not the right solution as it will result in
> > > Adding times in different units with NO_HZ enabled.
> 
> Yes, you are right. Looks like I've patched the wrong half of the
> inconsistency :-(
> I think it's a bit irritating you are using cputime64_t to store
> microseconds. At least it fooled me (I'm no kernel guy though) into
> thinking that get_cpu_idle_time_jiffy() returning jiffies was the
> intended behaviour.

Agreed. That cputime64 is ugly. There is also some confusion with naming
of get_cpu_idle_time_jiffy and get_cpu_idle_time_us and these routines
being redundantly repeated across 2 files. Will add them to my todo
queue.

> 
> > Does the below test patch (only compile tested) resolve the problem you
> > are seeing?
> 
> I've just rebooted the machine with the new patched kernel, and
> it looks good.

Ok. Thanks for reporting (and diagnosing as well :)) and verifying the
patch. I will resend the patch with a bit more description and your
Reported/Tested-by.

Thanks,
Venki


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