Re: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree

[Mark Lord]

Pallipadi, Venkatesh wrote:
>  
>
> > -----Original Message-----
> > From: Mark Lord [mailto:lkml@xxxxxx] 
> > Sent: Wednesday, January 02, 2008 3:42 PM
> > To: Arjan van de Ven
> > Cc: Pallipadi, Venkatesh; Andrew Morton; abelay@xxxxxxxxxx; 
> > lenb@xxxxxxxxxx; Ingo Molnar; linux-kernel@xxxxxxxxxxxxxxx; 
> > linux-acpi@xxxxxxxxxxxxxxx
> > Subject: Re: + restore-missing-sysfs-max_cstate-attr.patch 
> > added to -mm tree
> >
> > Arjan van de Ven wrote:
> > > On Fri, 30 Nov 2007 22:31:17 -0500
> > > Mark Lord <lkml@xxxxxx> wrote:
> > >
> > > > Arjan van de Ven wrote:
> > > > > On Fri, 30 Nov 2007 22:14:08 -0500
> > > > > Mark Lord <lkml@xxxxxx> wrote:
> > > > >
> > > > > > > in -mm there is.. the QoS stuff allows you to set maximum
> > > > > > > tolerable
> > > > > > ..
> > > > > >
> > > > > > That's encouraging, I think, but not for 2.6.24.
> > > > > >
> > > > > > > latency. If your app cant take any latency, you should set
> > > > > > > those... and the side effect is that the kernel will not do
> > > > > > > long-latency C-states or P-state transitions..
> > > > > > ..
> > > > > >
> > > > > > I don't mind the cpufreq changing (actually, I want it to drop in
> > > > > > cpugfreq to save power and keep the fan off), but the 
> > C-states just
> > > > > > kill this app.
> > > > > >
> > > > > > The app is VMware.  I force the max_state=1 when launching,
> > > > > ah but then its' even easier... and can be done in 2.6.24 already.
> > > > > VMWare after all has a kernel module, and the latency stuff is in
> > > > > 2.6.23 and 2.6.24 available inside the kernel already.
> > > > ..
> > > >
> > > > Oh, I'm perfectly happy to write my own kernel module if that's what
> > > all you need to do in your kernel module is call
> > >
> > > add_latency_constraint("mark_wants_his_mouse", 5);
> > >
> > > or so
> > ..
> >
> > Dredging up an old regression again now:
> >
> > The "make my own module to replace /sys/.../max_cstate" doesn't work
> > for the single-core machine we use a lot around here.
> >
> > VMware is totally sluggish unless I go to another text window 
> > and do this:
> >
> >    while ( true ); do echo -n ; done
> >
> > At which point VMware performs well again,
> > the same as with "echo 1 > max_cstate" in 2.6.23.
> >
> > Anyone got any suggestions on how to fix this regression
> > or work around it for 2.6.24 ?
>
> Easiest and clean way to do it is to have a driver with
> set_acceptable_latency() for 1uS or so in init and
> remove_acceptable_latency() at exit.
..

As noted, I already do that.  It helps with my Core2Duo machine,
but not with the single-core case.  Bummer.

-ml
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