linux-kernel - Re: [PATCH 08/12] perf: export some syscall metadata

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Message-ID: <20100225024259.GD7491@nowhere>
Date:	Thu, 25 Feb 2010 03:43:00 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Tom Zanussi <tzanussi@...il.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, rostedt@...dmis.org,
	k-keiichi@...jp.nec.com
Subject: Re: [PATCH 08/12] perf: export some syscall metadata

On Wed, Feb 24, 2010 at 12:00:43AM -0600, Tom Zanussi wrote:
> Re event injection - I don't know that much about it, but if it can be
> used for this, could it also be applied to the rest of the trace and
> header data too?  If so, that would enable 'live mode' tracing.  I
> already have a working prototype that does it by converting all those
> things into synthesized pseudo-events, but it would be nicer to use the
> event injection framework instead, if I understand it correctly...

I'm not sure what you mean about live mode tracing. But yeah this
about synthetizing pseudo-events. The purpose is to catchup with
"past events" or "dead events".

The first trial was for lock_init events. Lock init events send
the address of the lock plus its name, so that subsequent lock
events (lock acquire, lock_release) can just send the address
in the event and not the name which can then be retrieved
from past lock_init events.

One problem though: when we enable the lock_init event, we
only catch the new locks created. So we need the previously
registered locks. There may be severals ways to do that: using
a perf ioctl or so, it's still in discussion.

But then for syscalls we would have a kind of dead events
catching up by asking the kernel to send us the nr:name
pairs.

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