linux-kernel - Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq

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Message-ID: <20140211194726.GA9987@twins.programming.kicks-ass.net>
Date:	Tue, 11 Feb 2014 20:47:26 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Len Brown <len.brown@...el.com>,
	Preeti Murthy <preeti.lkml@...il.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>
Subject: Re: [RFC PATCH 3/3] idle: store the idle state index in the struct rq

On Tue, Feb 11, 2014 at 09:12:02AM -0800, Arjan van de Ven wrote:
> On 2/11/2014 8:41 AM, Peter Zijlstra wrote:
> >On Mon, Feb 03, 2014 at 08:17:47AM -0800, Arjan van de Ven wrote:
> >>On 2/3/2014 6:56 AM, Peter Zijlstra wrote:
> >>if there's a simple api like
> >>
> >>sched_cpu_cache_wiped(int llc)
> >>
> >>that would be very nice for this; the menuidle side knows this
> >>for some cases and thus can just call it. This would be a very
> >>small and minimal change
> >>
> >>* if you don't care about llc vs core local caches then that
> >>   parameter can go away
> >>
> >>* I assume this is also called for the local cpu... if not then we
> >>   need to add a cpu number argument
> >>
> >>* we can also call this from architecture code when wbinvd or the
> >>   arm equivalent is called etc
> >
> >A little something like so?
> >
> 
> is there value also in doing a cpu level cache flush?
> (cpu cache flush we know from the C state, for the llc cache flush we need to read an MSR
> on x86. Not insane expensive but not zero either)

L1 or L2? L1 is too small to really bother afaik and L2 is shared
between logical cpus so we'd need a mask there, not sure the generic
topology has that.

I'll have a quick peek later.
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