Re: [PATCH] cpufreq fix timer teardown in conservative governor(2.6.30-rc2)

From: Mathieu Desnoyers
Date: Sun Apr 26 2009 - 12:36:59 EST


* Henrique de Moraes Holschuh (hmh@xxxxxxxxxx) wrote:
> On Fri, 24 Apr 2009, Mathieu Desnoyers wrote:
> > * Len Brown (lenb@xxxxxxxxxx) wrote:
> > > Somebody please remind me why we are spending effort to
> > > maintain the conservative governor instead of deleting it.
> >
> > Documentation/cpu-freq/governors.txt
> >
> > "The CPUfreq governor "conservative", much like the "ondemand"
> > governor, sets the CPU depending on the current usage. It differs in
> > behaviour in that it gracefully increases and decreases the CPU speed
> > rather than jumping to max speed the moment there is any load on the
> > CPU. This behaviour more suitable in a battery powered environment."
> >
> > So better battery usage seems to be the reason why conservative lives.
>
> Yeah, but the question is: is it really better in practice? race-to-idle
> works better with ondemand. Note: that needs to be answered not just for
> the current crop of mobile processors, but also for at least stuff as old as
> the Pentium M and Pentium 4 M.
>
> What it _does_ help, is in broken !@#$ hardware that makes a lot of noise
> due to "singing capacitors" if you use ondemand (because conservative will
> make less noise as it causes more smooth transitions). NOHZ helped a great
> deal there, too.
>

I effectively have such singing capacitors on my laptop, and I still
have good ears.

> I don't know if there are battery environments where a harsher work profile
> by the CPU are a bad idea. If there are any, conservative will also help
> there.
>

Good question. We might also consider that anyway code duplication
between ondemand and conservative is a bad thing. Those look so similar
that part of them should probably be merged, with a sysfs flag and
kernel parameter to select the behavior.

Mathieu


> --
> "One disk to rule them all, One disk to find them. One disk to bring
> them all and in the darkness grind them. In the Land of Redmond
> where the shadows lie." -- The Silicon Valley Tarot
> Henrique Holschuh

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/