linux-kernel - Re: [RFCv2 0/8] perf tool: Add new event group management

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Date:	Mon, 28 May 2012 21:21:57 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Ulrich Drepper <drepper@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, acme@...hat.com,
	a.p.zijlstra@...llo.nl, mingo@...e.hu, paulus@...ba.org,
	cjashfor@...ux.vnet.ibm.com, fweisbec@...il.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [RFCv2 0/8] perf tool: Add new event group management

On Sun, May 27, 2012 at 03:56:22AM -0400, Ulrich Drepper wrote:
> On Sat, May 26, 2012 at 8:38 AM, Jiri Olsa <jolsa@...hat.com> wrote:
> > If you have some ideas on this or real world examples,
> > that would really help.. so far, here's the latest discussion:
> > http://marc.info/?t=133357436900005&r=1&w=2
> 
> If you're looking for a definitive source, just point to the Intel
> optimization manual.  Absolute values of counters are not really
> useful and so they are defining many (50+) ratios which people should
> investigate.  These ratios are only really accurate if the counters
> are swapped in and out at the same time.

thanks a lot for the pointer, very useful

> 
> The reminds me of a detail I looked at when starting an an
> implementation for this (glad you got more time to devote to it).  The
> problem with ratios are that there are so many.  So efficient
> scheduling is going to be important.  Many ratios use as a base the
> same counters over and over again (e.g., cycle count, instruction
> count, etc).  Therefore it is important to recognize when two groups
> can be scheduled concurrently even if the total number of counters
> needed would be high but due to intersections it is possible.
> 
> One last comment, not critical.  From a parsing point of view the
> colon in the proposed syntax
> 
>     name : { counter1, counter2 }
> 
> is unnecessary.  Just one more thing people can get wrong.  How about
> leaving it out?  An open curly brace to indicate a group should be
> sufficient.

yep, we'll omit the first colon

I'll CC you guys on next patchset

thanks,
jirka
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