linux-kernel - Re: [PATCH 5/5] perf, x86: Add support for AMD family 15h core counters

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Date:	Thu, 03 Feb 2011 10:38:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Robert Richter <robert.richter@....com>
Cc:	Stephane Eranian <eranian@...gle.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] perf, x86: Add support for AMD family 15h core
 counters

On Thu, 2011-02-03 at 10:00 +0100, Robert Richter wrote:
> 
> 
> ok, nb events may be implemented independent from core events in a
> separate struct pmu.
> 
> I still would prefer a lookup table for counter addresses. Adding a
> shift parameter to struct x86_pmu to do a
> 
>       addr = base + (index << shift)
> 
> seems to me a quite special solution that may not be reused in other
> implementations

What other implementations? I hope people will not re-arrange the MSR
layout on every new model, that'd be quite annoying.

>  while a lookup table is more generic. I also don't
> see a performance or memory impact there.

Well it is an extra pointer chase and data cache hit just to get
something you can trivially compute.

> Anyway, a shift parameter would work too. What do you think? 

I think the alternatives thing is probably nicest, except for having to
write the bits in asm.

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