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

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Date:	Wed, 23 Sep 2015 19:07:53 +0000
From:	"Liang, Kan" <kan.liang@...el.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
CC:	"acme@...nel.org" <acme@...nel.org>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"namhyung@...nel.org" <namhyung@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <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?

Right, --counter-read-interval is independent of sampling freq.
If we set --counter-read-interval to 10ms, it will read counter every 10ms
no matter what sampling frequency is set.

Thanks,
Kan
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