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DateWed, 2 Jan 2008 16:51:57 -0800
FromAndrew Morton <>
SubjectRe: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree
On Wed, 2 Jan 2008 16:06:20 -0800 "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com> wrote:

> > > >-----Original Message-----> >From: Mark Lord [mailto:lkml@rtr.ca] > >Sent: Wednesday, January 02, 2008 3:42 PM> >To: Arjan van de Ven> >Cc: Pallipadi, Venkatesh; Andrew Morton; abelay@novell.com; 
> >lenb@kernel.org; Ingo Molnar; linux-kernel@vger.kernel.org; 
> >linux-acpi@vger.kernel.org> >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@rtr.ca> wrote:
> >> 
> >>> Arjan van de Ven wrote:> >>>> On Fri, 30 Nov 2007 22:14:08 -0500> >>>> Mark Lord <lkml@rtr.ca> 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.

err, you appear to be suggesting that Mark patch his kernel to make it work
as well as 2.6.23?  That would be a wrong answer.

This regression was known six weeks ago.  What do we need to do (or revert)
to fix it in 2.6.24?



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