linux-kernel - Re: [Cbe-oss-dev] [RFC, PATCH 4/4] Add support to OProfile for profiling Cell BE SPUs -- update

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Date:	Wed, 31 Jan 2007 10:34:03 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	maynardj@...ibm.com
Cc:	linuxppc-dev@...abs.org, oprofile-list@...ts.sourceforge.net,
	cbe-oss-dev@...abs.org, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [Cbe-oss-dev] [RFC, PATCH 4/4] Add support to OProfile for
	profiling Cell BE SPUs -- update


> I've given this some more thought, and I'm coming to the conclusion that 
> a pure array-based implementation for holding cached_info (getting rid 
> of the lists) would work well for the vast majority of cases in which 
> OProfile will be used.  Yes, it is true that the mapping of an SPU 
> context to a phsyical spu-numbered array location cannot be guaranteed 
> to stay valid, and that's why I discard the cached_info at that array 
> location when the SPU task is switched out.  Yes, it would be terribly 
> inefficient if the same SPU task gets switched back in later and we 
> would have to recreate the cached_info.  However, I contend that 
> OProfile users are interested in profiling one application at a time. 
> They are not going to want to muddy the waters with multiple SPU apps 
> running at the same time.  I can't think of any reason why someone would 
> conscisouly choose to do that.
> 
> Any thoughts from the general community, especially OProfile users?

Well, it's my understanding that quite a few typical usage scenario
involve different tasks running on different SPUs passing each other
data around.

Ben.


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