linux-kernel - Re: [PATCH 0/2] x86/intel_rdt and perf/x86: Fix lack of coordination with perf

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Message-ID: <20180802173727.GP2494@hirez.programming.kicks-ass.net>
Date:   Thu, 2 Aug 2018 19:37:27 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, fenghua.yu@...el.com,
        tony.luck@...el.com, vikas.shivappa@...ux.intel.com,
        gavin.hindman@...el.com, jithu.joseph@...el.com,
        dave.hansen@...el.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] x86/intel_rdt and perf/x86: Fix lack of coordination
 with perf

On Thu, Aug 02, 2018 at 09:44:13AM -0700, Reinette Chatre wrote:
> On 8/2/2018 9:18 AM, Peter Zijlstra wrote:
> > On Thu, Aug 02, 2018 at 09:14:10AM -0700, Reinette Chatre wrote:
> > 
> >> The current implementation does not coordinate with perf and this is
> >> what I am trying to fix in this series.
> >>
> >> I do respect your NAK but it is not clear to me how to proceed after
> >> obtaining it. Could you please elaborate on what you would prefer as a
> >> solution to ensure accurate measurement of cache-locked data that is
> >> better integrated?
> > 
> > We have an in-kernel interface to perf, use that if you want access to
> > the PMU. You will not directly stomp on PMU registers.
> 
> I do not see how I can do so without incurring the cache hits and misses
> from the data needed and instructions run by this interface. Could you
> please share how I can do so and still obtain the accurate measurement
> of cache residency of a specific memory region?

That's the best you're going to get. You do _NOT_ get to use raw PMU.