linux-kernel - Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)

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Date:	Wed, 21 Dec 2011 14:22:33 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	Robert Richter <robert.richter@....com>,
	Benjamin Block <bebl@...eta.org>,
	Hans Rosenfeld <hans.rosenfeld@....com>, hpa@...or.com,
	tglx@...utronix.de, suresh.b.siddha@...el.com, eranian@...gle.com,
	brgerst@...il.com, Andreas.Herrmann3@....com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Benjamin Block <benjamin.block@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)


* Avi Kivity <avi@...hat.com> wrote:

> On 12/21/2011 02:34 PM, Ingo Molnar wrote:
>
> > I think it can all be supported in a consistent way (see my 
> > previous mails) - but the feature as presented today just 
> > does not look useful enough to me if only supports that 
> > niche self-monitoring usecase.
> 
> I hate to re-enter this thread, but this "niche use case" is 
> exactly what LWP is designed for. [...]

It's not the only usecase that it can be used in, and that is 
what matters to me.

> [...] And once the JVM is adapted to exploit LWP, its use will 
> dwarf all of the uses of perf put together (except the NMI 
> watchdog).  You're only causing the developers needless pain 
> by forcing them to fit this red peg into a green hole.

I disagree - i think LWP has been seriously over-sold and 
seriously under-designed. Anyway, i'm willing to be convinced 
that it's worth to be merged upstream, if it brings tangible 
benefits to the usecases i mentioned.

Thanks,

	Ingo
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