From: David Ahern <dsahern@gmail.com>
To: Stephane Eranian <eranian@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, mingo@elte.hu, acme@infradead.org,
robert.richter@amd.com, ming.m.lin@intel.com,
andi@firstfloor.org, asharma@fb.com, ravitillo@lbl.gov,
vweaver1@eecs.utk.edu
Subject: Re: [PATCH 00/13] perf_events: add support for sampling taken branches (v3)
Date: Tue, 24 Jan 2012 09:08:32 -0700 [thread overview]
Message-ID: <4F1ED780.3010305@gmail.com> (raw)
In-Reply-To: <CABPqkBSALpYBTpaJo4Wor6weM-XM3PRxj23u8N+Kihvm36Hj8w@mail.gmail.com>
On 01/24/2012 08:39 AM, Stephane Eranian wrote:
> Hi,
>
> The branch stack sampling patch exposes a flaw in the sampling
> buffer format as currently exported by the kernel.
>
> In the current format, sample records (RECORD_SAMPLE) are NOT
> self-describing. That means that by looking at the fixed size header, it
> is not possible to determine which event caused the sample to be recorded
> and what's in the body of the variable length sample.
>
> Such introspection is only possible once we know the event unique id
> (PERF_SAMPLE_ID). But to get the event ID, we need to parse the
> sample. But, given that a sample has a variable length, there is no
> predefined position for that ID in the sample. You have a chicken
> and egg problem here. There is no room left in the fixed size header
> to fit this in.
I brought this up last Fall as well. As I recall the response is to move
each sample_type based stream into its own data file and then merge the
data files while processing.
David
next prev parent reply other threads:[~2012-01-24 16:08 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-09 16:49 [PATCH 00/13] perf_events: add support for sampling taken branches (v3) Stephane Eranian
2012-01-09 16:49 ` [PATCH 01/13] perf_events: add generic taken branch sampling support (v3) Stephane Eranian
2012-01-27 4:46 ` Anshuman Khandual
2012-01-27 9:57 ` Stephane Eranian
2012-01-09 16:49 ` [PATCH 02/13] perf_events: add Intel LBR MSR definitions (v3) Stephane Eranian
2012-01-27 5:03 ` Anshuman Khandual
2012-01-09 16:49 ` [PATCH 03/13] perf_events: add Intel X86 LBR sharing logic (v3) Stephane Eranian
2012-01-09 16:49 ` [PATCH 04/13] perf_events: sync branch stack sampling with X86 precise_sampling (v3) Stephane Eranian
2012-01-27 5:26 ` Anshuman Khandual
2012-01-09 16:49 ` [PATCH 05/13] perf_events: add LBR mappings for PERF_SAMPLE_BRANCH filters (v3) Stephane Eranian
2012-01-27 5:41 ` Anshuman Khandual
2012-01-09 16:49 ` [PATCH 06/13] perf_events: disable LBR support for older Intel Atom processors (v3) Stephane Eranian
2012-01-27 5:43 ` Anshuman Khandual
2012-01-09 16:49 ` [PATCH 07/13] perf_events: implement PERF_SAMPLE_BRANCH for Intel X86 (v3) Stephane Eranian
2012-01-27 6:14 ` Anshuman Khandual
2012-01-09 16:49 ` [PATCH 08/13] perf_events: add LBR software filter support " Stephane Eranian
2012-01-09 16:49 ` [PATCH 09/13] perf_events: disable PERF_SAMPLE_BRANCH_* when not supported (v3) Stephane Eranian
2012-01-27 7:15 ` Anshuman Khandual
2012-01-27 9:56 ` Stephane Eranian
2012-01-09 16:49 ` [PATCH 10/13] perf_events: add hook to flush branch_stack on context switch (v3) Stephane Eranian
2012-01-09 16:49 ` [PATCH 11/13] perf: add code to support PERF_SAMPLE_BRANCH_STACK (v3) Stephane Eranian
2012-01-10 1:25 ` Arun Sharma
2012-01-10 15:43 ` Stephane Eranian
2012-01-09 16:49 ` [PATCH 12/13] perf: add support for sampling taken branch to perf record (v3) Stephane Eranian
2012-01-09 16:49 ` [PATCH 13/13] perf: add support for taken branch sampling to perf report (v3) Stephane Eranian
2012-01-23 10:14 ` [PATCH 00/13] perf_events: add support for sampling taken branches (v3) Stephane Eranian
2012-01-23 12:25 ` Peter Zijlstra
2012-01-23 15:07 ` Stephane Eranian
2012-01-23 15:47 ` Andi Kleen
2012-01-23 17:14 ` Stephane Eranian
2012-01-24 15:39 ` Stephane Eranian
2012-01-24 16:08 ` David Ahern [this message]
2012-01-24 17:42 ` Stephane Eranian
2012-01-26 16:21 ` Stephane Eranian
2012-01-27 12:09 ` Peter Zijlstra
2012-01-27 18:20 ` Arun Sharma
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