linux-kernel - Re: Unified tracing buffer

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Date:	Mon, 22 Sep 2008 20:04:37 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Darren Hart <darren@...art.com>
CC:	Martin Bligh <mbligh@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <compudj@...stal.dyndns.org>,
	Steven Rostedt <rostedt@...dmis.org>, od@...ell.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	systemtap-ml <systemtap@...rces.redhat.com>
Subject: Re: Unified tracing buffer

Hi Darren,

Darren Hart wrote:
> On Mon, Sep 22, 2008 at 3:25 PM, Masami Hiramatsu <mhiramat@...hat.com> wrote:
> 
>>> One thing that I think is still important is to have a unified timestamp
>>> mechanism on everything, so we can co-ordinate different things back
>>> together in userspace from different trace tools, so I intend to keep
>>> that at a lower level, but I think you're right that the event id, etc can
>>> move up into separate layers.
>> I'm not so sure that the unified 'timestamp' must be required by all tracers.
>> If you just need to merge and sort per-cpu data, you can use an atomic
>> sequential number for it.
>> IMHO, the unified 'timestamp' would better be an option, because some
>> architectures can't support it. I think preparing timestamp-callback
>> function will help us.
>>
> 
> There have been several posts on the timestamp for the events.  From a
> real-time perspective, this timestamp will be a very important datapoint for
> each event, and the more accurate/higher resolution the better.  Some thoughts.

Sure, I know the precise timestamp is required for real-time sensitive
tracers. however, there are some other cases. for example debugging,
we don't need timestamps, but just want to know the order of events. :-)

Thank you,

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@...hat.com

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