Re: [PATCH 25/32] sched: introduce the finish_arch_pre_lock_switch() scheduler hook

[Vikas Shivappa]

On Fri, 29 Apr 2016, David Carrillo-Cisneros wrote:

> (Re-sending in plain text)
>
> This hook is used in the following patch in the series to write to
> PQR_ASSOC_MSR, a msr that is utilized both by CQM/CMT and by CAT.
> Since CAT is not dependent on perf, I created this hook to start CQM
> monitoring right after other events start while keeping it independent
> of perf. The idea is to have future versions of CAT to also rely on
> this hook.

CAT did the msr write in switch_to as Peter did not want a new hook to be used. 
Same could be done here.

Thanks,
Vikas

> On Fri, Apr 29, 2016 at 11:05 AM, David Carrillo-Cisneros
> <davidcc@xxxxxxxxxx> wrote:
> > This hook is used in the following patch in the series to write to
> > PQR_ASSOC_MSR, a msr that is utilized both by CQM/CMT and by CAT. Since CAT
> > is not dependent on perf, I created this hook to start CQM monitoring right
> > after other events start while keeping it independent of perf. The idea is
> > to have future versions of CAT to also rely on this hook.
> >
> > On Fri, Apr 29, 2016 at 1:52 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > > On Thu, Apr 28, 2016 at 09:43:31PM -0700, David Carrillo-Cisneros wrote:
> > > > This hook allows architecture specific code to be called at the end of
> > > > the task switch and after perf_events' context switch but before the
> > > > scheduler lock is released.
> > > >
> > > > The specific use case in this series is to avoid multiple writes to a
> > > > slow
> > > > MSR until all functions which modify such register in task switch have
> > > > finished.
> > >
> > > Yeah, no. This really need way more justification. Why can't you use the
> > > regular perf sched-in stuff for CQM?