linux-kernel - Re: [RFC PATCH] perf: Add load latency monitoring on Intel Nehalem/Westmere

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Message-ID: <1293099498.2170.452.camel@laptop>
Date:	Thu, 23 Dec 2010 11:18:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Lin Ming <ming.m.lin@...el.com>
Cc:	Stephane Eranian <eranian@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Arjan van de Ven <arjan@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>, paulus <paulus@...ba.org>
Subject: Re: [RFC PATCH] perf: Add load latency monitoring on Intel
 Nehalem/Westmere

On Thu, 2010-12-23 at 16:59 +0800, Lin Ming wrote:
> > {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}. 

That is most certainly a very valid encoding, and a rather nice one at
that. I hadn't really gone further than: 4*3*2 + 3 < 2^5 :-)

If you also make OTHER=0, then a valid encoding for unknown is also 0,
which is a nice meaning for 0...
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