lkml.org 
[lkml]   [2014]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRE: [PATCH v2] ARM: perf: save/restore pmu registers in pm notifier
Will,
Thanks for the comments!

> -----Original Message-----
> From: Will Deacon [mailto:will.deacon@arm.com]
> Sent: 2014年4月15日 16:48
> To: Neil Zhang
> Cc: linux@arm.linux.org.uk; linux-arm-kernel@lists.infradead.org;
> linux-kernel@vger.kernel.org; Sudeep Holla
> Subject: Re: [PATCH v2] ARM: perf: save/restore pmu registers in pm notifier
>
> Hello,
>
> On Mon, Apr 14, 2014 at 02:42:22AM +0100, Neil Zhang wrote:
> > From: Sudeep KarkadaNagesha <sudeep.karkadanagesha@arm.com>
> >
> > This adds core support for saving and restoring CPU PMU registers for
> > suspend/resume support i.e. deeper C-states in cpuidle terms.
> > This patch adds support only to ARMv7 PMU registers save/restore.
> > It needs to be extended to xscale and ARMv6 if needed.
> >
> > [Neil] We found that DS-5 not work on our CA7 based SoCs.
> > After debuging, found PMU registers were lost because of core power down.
> > Then i found Sudeep had a patch to fix it about two years ago but not
> > in the mainline, just port it.
>
> What I don't like about this patch is that we're introducing significant
> overhead for SoCs that don't require save/restore of the PMU state. I'd much
> rather see core power down disabled whilst the PMU is in use but, if that's not
> possible, then I think we need to:
>
> (1) Make this conditional for cores that really need it
>
> (2) Only save/restore if the PMU is in use (even better, just save/restore
> the live registers, but that's probably not worth the effort
> initially).
>

The patch has check the ARMV7_PMNC_E bit when save / restore,
so suppose only the core's that use PMU will do the save / restore work.

> (3) Ensure we ->reset the PMU before doing the restore

Ok, I can add it in the next version.

>
> Will

Best Regards,
Neil Zhang

\
 
 \ /
  Last update: 2014-04-15 15:21    [W:0.085 / U:36.600 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site