linux-kernel - Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS

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Date:	Mon, 2 Mar 2015 17:23:35 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	Stephane Eranian <eranian@...gle.com>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Jiri Olsa <jolsa@...hat.com>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
	linux-man@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Chuck Ebbert <cebbert.lkml@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [patch] perf_event_open.2: 3.19 PERF_SAMPLE_REGS_INTR support

On Mon, 2 Mar 2015, Stephane Eranian wrote:


> Vince, REGS_USER is user ONLY. It does not capture machine state if PMU
> interrupt occurred inside the kernel. REGS_USER is useful in support of dwarf
> based user level call stack unwinding. Otherwise REGS_INTR is what most
> analysis tools need.

so the summary is:

	REGS_USER : gives you the registers at the time of interrupt,
			but always in user mode (if in kernel reports
			last ip before entered kernel)
			useful for stack unwinding

	REGS_INTR and precise_ip=0:
			same as REGS_USER

	REGS_INTR and precise_ip>0 and PEBS hardware:
			gives you the register state at time
			of interrupt.  Can be inside of kernel.


	do not enable REGS_USER and REG_INTR at the same time
		as REGS_USER will have REG_INTR values and
		cannot be used for user stack unwinding

Vince
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