linux-kernel - Re: [PATCH RFC 06/10] perf,tools: option to set counter read interval

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Date:	Wed, 23 Sep 2015 11:55:06 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	kan.liang@...el.com
Cc:	acme@...nel.org, jolsa@...nel.org, a.p.zijlstra@...llo.nl,
	mingo@...hat.com, namhyung@...nel.org, ak@...ux.intel.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 06/10] perf,tools: option to set counter read interval

kan.liang@...el.com [kan.liang@...el.com] wrote:
| From: Kan Liang <kan.liang@...el.com>
| 
| Add a timer to read counter regularly. Option --counter-read-interval
| can be used to set the interval.
| Only read counter statistics at the beginning and the end is not enough.
| Sometimes, we need fine granularity to do sophisticated analysis. For
| example,10-20ms is required to do sophisticated bandwidth analysis.
| 
| Signed-off-by: Kan Liang <kan.liang@...el.com>
| ---
|  tools/perf/Documentation/perf-record.txt |  8 +++++++
|  tools/perf/builtin-record.c              | 37 ++++++++++++++++++++++++++++++++
|  2 files changed, 45 insertions(+)
| 
| diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
| index 2e9ce77..c1d9024 100644
| --- a/tools/perf/Documentation/perf-record.txt
| +++ b/tools/perf/Documentation/perf-record.txt
| @@ -308,6 +308,14 @@ This option sets the time out limit. The default value is 500 ms.
|  Record context switch events i.e. events of type PERF_RECORD_SWITCH or
|  PERF_RECORD_SWITCH_CPU_WIDE.
| 
| +--counter-read-interval::
| +Sets the interval to do counter read regularly. This option is only valid

How about "Sets the interval at which the counter should be read"?

| +with counter read event (:C). This option is disabled by default. It means
| +that the event counter can only be read at the beginning and the end.

Should this last sentence be: "When this option is disabled, the event
counter can only be read at the beginning and the end?"

| +This option could be used when we need fine granularity to do sophisticated
| +analysis. For example, 10-20ms is required to do sophisticated memory
| +bandwidth analysis.

I guess this is independent of the sampling frequency (perf-record -F)? 

IOW, is the need for --counter-read-interval so we can sample at one
frequency, but read the counter values/statistics at a different frequency?

Sukadev

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