Message-ID: <557AECB4.5050709@gmail.com>
Date: Fri, 12 Jun 2015 08:29:08 -0600
From: David Ahern <dsahern@gmail.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version: 1.0
To: Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>
CC: Andi Kleen <ak@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org,
        Jiri Olsa <jolsa@redhat.com>, Stephane Eranian <eranian@google.com>,
        mathieu.poirier@linaro.org, Pawel Moll <pawel.moll@arm.com>
Subject: Re: [RFC PATCH] perf: Add PERF_RECORD_SWITCH to indicate context
 switches
References: <1433859670-10806-1-git-send-email-adrian.hunter@intel.com> <20150611141548.GW19282@twins.programming.kicks-ass.net> <557ABE8B.1020705@intel.com>
In-Reply-To: <557ABE8B.1020705@intel.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1554
Lines: 30

On 6/12/15 5:12 AM, Adrian Hunter wrote:
>>> This new PERF_RECORD_SWITCH event does not have those problems
>>> and it also has a couple of other small advantages. It is
>>> easier to use because it is an auxiliary event (like mmap,
>>> comm and task events) which can be enabled by setting a single
>>> bit. It is smaller than sched:sched_switch and easier to parse.
>>
>> Right, so the one wee problem I have is that this only provides sched_in
>> data, I imagine people might be interested in sched_out as well.
>
> That is not a problem although it would be interesting to know the use-case.
> To me it seemed unreasonable to expect to analyze scheduler behaviour
> without admin-level privileges since it is inherently an administrative
> activity.

One use case is wanting to analyze a set of processes -- how long they 
run when scheduled, where they are when scheduled out, scheduling delay 
on wakeups, time between scehd in. I wrote the timehist tool in 2010 it 
has been really helpful understanding what is happening on each cpu and 
characteristics of a set of processes (e.g. ping ponging between tasks 
sending messages to each other).

In this case it is not necessarily scheduler behavior (though it does it 
enter the picture to a degree), but rather behavior of a process or set 
of tasks.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/