linux-kernel - RE: [patch] x86, perf_counter, bts: add bts to perf

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Message-ID: <928CFBE8E7CB0040959E56B4EA41A77EC1BFF05E@irsmsx504.ger.corp.intel.com>
Date:	Fri, 7 Aug 2009 12:34:46 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...or.com" <hpa@...or.com>,
	"markus.t.metzger@...il.com" <markus.t.metzger@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [patch] x86, perf_counter, bts: add bts to perf_counter

>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@...e.hu]
>Sent: Friday, August 07, 2009 1:20 PM
>To: Metzger, Markus T
>Cc: Peter Zijlstra; tglx@...utronix.de; hpa@...or.com; markus.t.metzger@...il.com; linux-
>kernel@...r.kernel.org
>Subject: Re: [patch] x86, perf_counter, bts: add bts to perf_counter
>
>
>note, i had this running in the background, as root:
>
>/home/mingo/bin/perf top >/dev/null 2>/dev/null&
>
>that is what interacted most likely.

I'll try that, as well.


> I killed that task and did a
>user-space only recording via:
>
>titan:~> perf record -f -e branches:u -c 1 ./loop_1b_instructions
>
>and that succeeded:
>
>^C[ perf record: Captured and wrote 827.901 MB perf.data (~36171547 samples) ]
>
>to make BTS sampling really practical we need a 'flight data
>recorder' mode for the mmap buffer (overwrite mode), right? Peter
>sent you a patch for that some time ago - did anything good happen
>to that patch?

You mean the patch to find the beginning of the buffer?

Seems that we only get one type of record in those buffers, so a debugger can read
the trace from tail to head.

I had been expecting that we can have multiple counters write into the same mmap
buffer, but when I actually tried to do that, it looked like I would need a separate
mmap buffer per counter.

thanks and regards,
markus.

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