linux-kernel - Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle candidate and the basis for SIS

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Date:   Sat, 03 Feb 2018 08:30:48 -0800
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Mike Galbraith <efault@....de>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        LKML <linux-kernel@...r.kernel.org>, Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 4/4] sched/fair: Use a recently used CPU as an idle
 candidate and the basis for SIS

On Fri, 2018-02-02 at 15:08 +0100, Peter Zijlstra wrote:
> On Fri, Feb 02, 2018 at 01:46:47PM +0100, Peter Zijlstra wrote:
> 
> > +static void __intel_pstate_hwp_set_desired(int val)
> > +{
> > +	u64 value;
> > +
> > +	value = rdmsrl(MSR_HWP_REQUEST);
> > +	value &= ~GENMASK_ULL(23, 16);
> > +	value |= (val & 0xff) << 16;
> > +	wrmsrl(MSR_HWP_REQUEST, val);
> > +}
> 
> Also, if we keep a software shadow of that MSR, we can avoid the
> rdmsr, which might also help.
The reason we don't keep a software shadow as users can use x86-energy-
perf utility or via BMC to adjust.  CCed  to Len.