linux-kernel - Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation

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Message-ID: <87oa3ar65b.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Mon, 26 Sep 2016 19:13:20 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org, vince@...ter.net, eranian@...gle.com,
        Arnaldo Carvalho de Melo <acme@...radead.org>,
        tglx@...utronix.de
Subject: Re: [RFC PATCH 1/6] perf: Move mlock accounting to ring buffer allocation

Peter Zijlstra <peterz@...radead.org> writes:

> On Mon, Sep 26, 2016 at 11:27:08AM +0300, Alexander Shishkin wrote:
>> Peter Zijlstra <peterz@...radead.org> writes:
>> 
>> > Well, we could 'force' inject a VMA into the process's address space, we
>> > do that for a few other things as well. It also makes for less
>> > exceptions with the actual core dumping.
>> 
>> Threads then will end up with the same buffer (through sharing the mm),
>> but they can't really share trace buffers.
>> 
>> Also, system core dump is still a problem.
>
> Hurm, true on both counts.

OTOH, system core dump buffers don't need inheritance or memlock
accounting.

>> Or we can have per-cpu buffers for all user's tasks, record where each
>> task starts and ends in each buffer and cut out only bits relevant to
>> the task(s) that dump core.
>
> Which gets you the problem that when a task dumps core there might not
> be any state in the buffer, because the previous task flushed it all out
> :/

And also won't work with PMUs that don't generate PMIs, like ETMs.

Regards,
--
Alex