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Subject: Re: [RFC PATCH] perf: Add load latency monitoring on Intel
 Nehalem/Westmere
From: Lin Ming <ming.m.lin@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>, Ingo Molnar <mingo@elte.hu>,
        Andi Kleen <andi@firstfloor.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Arjan van de Ven <arjan@infradead.org>,
        lkml <linux-kernel@vger.kernel.org>, paulus <paulus@samba.org>
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Date: Thu, 23 Dec 2010 16:59:41 +0800
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On Wed, 2010-12-22 at 18:49 +0800, Peter Zijlstra wrote:
> On Wed, 2010-12-22 at 11:45 +0100, Peter Zijlstra wrote:
> > On Wed, 2010-12-22 at 11:08 +0100, Stephane Eranian wrote:
> > > Yes, I think there is more to it than just data source, unfortunately.
> > > If you want to avoid returning an opaque u64 (PERF_SAMPLE_EXTRA), then
> > > you need to break it down: PERF_SAMPLE_DATA_SRC, PERF_SAMPLE_XX
> > > and so on. 
> > 
> > I guess we can do things like:
> > 
> > Satisfied by {L1, L2, L3, RAM}x{snoop, local, remote} + unknown, and
> > encode "Pending core cache HIT" as L2-snoop or something, whatever is
> > most appropriate.
> 
> Ah, I just saw my email window covered part of the spec and we can also
> have x{shared,exclusive}, so we end up with:
> 
> {L1, L2, L3, RAM}x{snoop, local, remote}x{shared, exclusive} + {unknown,
> uncached, IO}
> 
> Which takes all of 5 bits to encode.

Do you mean below encoding?

bits4 3 2 1 0
    + + + + +
    | | | | |
    | | | {L1, L2, L3, RAM} or {unknown, uncached, IO}
    | | |
    | {snoop, local, remote, OTHER}
    |
    {shared, exclusive}

If bits(2-3) is OTHER, then bits(0-1) is the encoding of {unknown,
uncached, IO}.

> 
> > But does that cover every architecture?
> > 
> > Also, since that doesn't require more that 4 bits to encode, we could
> > try and categorize what else is around and try and create a well
> > specified _EXTRA register, I mean, we still got 60bits left after this.
> 
> Leaving us with 59 bits to consider.