Re: [RFC][PATCH] perf: Implement read_group() PMU operation

From: Cody P Schafer
Date: Sun Feb 22 2015 - 16:04:54 EST

On Thu, Feb 5, 2015 at 9:59 PM, Sukadev Bhattiprolu
<sukadev@xxxxxxxxxxxxxxxxxx> wrote:
> From: Sukadev Bhattiprolu <sukadev@xxxxxxxxxxxxxxxxxx>
> Date: Thu Feb 5 20:56:20 EST 2015 -0300
> Subject: [RFC][PATCH] perf: Implement read_group() PMU operation
> This is a lightly tested, exploratory patch to allow PMUs to return
> several counters at once. Appreciate any comments :-)

Back when I was fiddling with this, I started looking into changing
the {start,commit,cancel}_txn to operate on (struct perf_event *)
rather than (struct pmu *), and commit_txn would generate the actual
request & reads based on the perf_event's group (sounds similar but
not identical to what Peter's proposed previously).

The key bit I was concerned about was that these "PMUs" aren't
actually physical hw, so it made a bit more sense to pin the grouping
to a group rather than a txn over a PMU.

[Of course, I never did confirm if that actually fit with how perf was
modeling txns]
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