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

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Date:	Mon, 19 Dec 2011 11:54:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	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>
Subject: Re: [RFC 4/5] x86, perf: implements lwp-perf-integration (rc1)


* Robert Richter <robert.richter@....com> wrote:

> On 19.12.11 00:43:10, Ingo Molnar wrote:
>
> > So the question becomes, how well is it integrated: can perf 
> > 'record -a + perf report', or 'perf top' use LWP, to do 
> > system-wide precise [user-space] profiling and such?
> 
> There is only self-monitoring of a process possible, no kernel 
> and system-wide profiling. This is because we can not allocate 
> memory regions in the kernel for a thread other than the 
> current. This would require a complete rework of mm code.

Hm, i don't think a rework is needed: check the 
vmalloc_to_page() code in kernel/events/ring_buffer.c. Right now 
CONFIG_PERF_USE_VMALLOC is an ARM, MIPS, SH and Sparc specific 
feature, on x86 it turns on if CONFIG_DEBUG_PERF_USE_VMALLOC=y.

That should be good enough for prototyping the kernel/user 
shared buffering approach.

Thanks,

	Ingo
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