linux-kernel - Re: [PATCH] perf: Add support for creating offline events

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Message-ID: <20180212210442.GA32093@krava>
Date:   Mon, 12 Feb 2018 22:04:42 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...eaurora.org>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        linux-kernel@...r.kernel.org, psodagud@...eaurora.org,
        tsoni@...eaurora.org
Subject: Re: [PATCH] perf: Add support for creating offline events

On Mon, Feb 12, 2018 at 09:42:05AM -0800, Raghavendra Rao Ananta wrote:
> Hi Jiri,
> 
> Thank you for the response.
> 
> Does perf tool has its own check to see if the CPU was offline during the
> lifetime of an event? If so, it might ignore these type of events.

nope, we don't check on that

> 
> Initially, I tested the same using perf tool and found similar results.
> Then I debugged further and found that the perf core was actually sending
> data to the userspace (copy_to_user()) and the corresponding count for the
> data. Hence, I tested this further by writing my own userspace application,
> and I was able to read the count through this,
> even when the CPU was made offline and back online.
> 
> Do you think we also have to modify the perf tool accordingly?

hum, I wonder what's wrong.. will check

jirka