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Re: Unified tracing buffer
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Darren Hart <darren at dvhart dot com>
- Cc: Martin Bligh <mbligh at google dot com>, Linux Kernel Mailing List <linux-kernel at vger dot kernel dot org>, Linus Torvalds <torvalds at linux-foundation dot org>, Thomas Gleixner <tglx at linutronix dot de>, Mathieu Desnoyers <compudj at krystal dot dyndns dot org>, Steven Rostedt <rostedt at goodmis dot org>, od at novell dot com, "Frank Ch. Eigler" <fche at redhat dot com>, systemtap-ml <systemtap at sources dot redhat dot com>
- Date: Mon, 22 Sep 2008 20:04:37 -0400
- Subject: Re: Unified tracing buffer
- References: <33307c790809191433w246c0283l55a57c196664ce77@mail.gmail.com> <48D7F5E8.3000705@redhat.com> <33307c790809221313s3532d851g7239c212bc72fe71@mail.gmail.com> <48D81B5F.2030702@redhat.com> <e17d46420809221611yeb107a1hd395770e4915b20@mail.gmail.com>
Hi Darren,
Darren Hart wrote:
> On Mon, Sep 22, 2008 at 3:25 PM, Masami Hiramatsu <mhiramat@redhat.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@redhat.com