RE: [PATCH] more robust halt_light

From: Alex Williamson <>
Date: 2004-03-04 08:08:00
   I was curious about that myself, but I thought I remembered from
Stephane that the perf counters didn't really recover from a
PAL_HALT_LIGHT on McKinley.  If that's not the case, maybe we can move
the PAL check into perfmon code, and it can selectively disable it as it
needs via the disable_hlt API.  I assume there are some cases were
perfmon wouldn't need to disable halt_light on working PAL, so the rev
check might not go away.


On Wed, 2004-03-03 at 13:38, Seth, Rohit wrote:
> The issue with performance counters is only when PAL_HALT_LIGHT is
> enabled.  It is nice to be able to use this power save feature when the
> performance counters are not currently/actively used system wide.  Can
> we use the disable_hlt and enable_hlt APIs (mentioned in the patch
> below) in perfmon kind of tools to disable/enable PAL_HALT_LIGHT
> whenever the system is transitioning in and out of system wide
> performance monitoring.  That way we don't have to have any tests for
> Mckinley, PAL versions etc. etc.
> rohit
> >-----Original Message-----
> >Sent: Wednesday, March 03, 2004 9:57 AM
> >To:
> >Subject: [PATCH] more robust halt_light
> >
> >
> >  This patch adds some i386-ish enable/disable features to the
> >pal_halt_light cpu idle implementation as well as tries to avoid bad
> >interactions with certain revs of PAL on McKinley cpus.  Hopefully this
> >will provide enough flexibility that we can leave it configured on in
> >the kernel by default.  My latest measurements on a 1.3GHz rx2600 show
> >that enabling pal_halt_light in the cpu_idle routine saves 23W/cpu on
> an
> >idle system.
> >
> >   FWIW, I added the enable/disable_hlt routines.  I don't see any
> >consumers of this for ia64 now, but it looked useful.  Patch against
> >latest linux-2.5 bk.  Thanks,
> >
> >	Alex
> >

Alex Williamson                             HP Linux & Open Source Lab

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Received on Wed Mar 3 16:10:41 2004

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