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Re: [Qemu-devel] [PATCH 2/5] trace-cmd: Use tracing directory to count C
From: |
Masami Hiramatsu |
Subject: |
Re: [Qemu-devel] [PATCH 2/5] trace-cmd: Use tracing directory to count CPUs |
Date: |
Thu, 23 Aug 2012 21:30:07 +0900 |
User-agent: |
Mozilla/5.0 (Windows NT 5.2; rv:13.0) Gecko/20120614 Thunderbird/13.0.1 |
(2012/08/23 18:08), Steven Rostedt wrote:
> On Thu, 2012-08-23 at 12:00 +0900, Masami Hiramatsu wrote:
>> (2012/08/23 11:01), Masami Hiramatsu wrote:
>>> (2012/08/22 22:41), Steven Rostedt wrote:
>>>> On Wed, 2012-08-22 at 17:43 +0900, Yoshihiro YUNOMAE wrote:
>>>>> From: Masami Hiramatsu <address@hidden>
>>>>>
>>>>> Count debugfs/tracing/per_cpu/cpu* to determine the
>>>>> number of CPUs.
>>>>
>>>> I'm curious, do you find that sysconf doesn't return the # of CPUs the
>>>> system has?
>>>
>>> No, sysconf returns the number of hosts CPUs, not guests.
>>>
>>>> I've had boxes where the per_cpu/cpu* had more cpus than the
>>>> box actually holds. But this was a bug in the kernel, not the tool. This
>>>> change log needs to have rational instead of just explaining what the
>>>> patch does.
>>>
>>> Ah, I see. Hmm, then this should be enabled by a command line
>>> option or an environment variable.
>>
>> Oops, I misunderstood. I'll add more comment for why this
>> should be tried instead of sysconf.
>
> And now that I understand why you are doing this, why not only do this
> if the TRACE_AGENT or DEBUG_TRACING_DIR is defined. That is, if we are
> doing it against a bare metal system, then sysconf should suffice, but
> if we are tracing against a guest, then it should use the tracing
> directory to determine the buffers.
>
> We could add options to override this, but I would think the default
> should just Do The Right Thing(tm).
Yeah, so I'd like to push this is the default method, and fix
the kernel bug (but I'm not sure that is a bug).
Thank you,
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: address@hidden
[Qemu-devel] [PATCH 3/5] trace-cmd: Support trace-agent of virtio-trace, Yoshihiro YUNOMAE, 2012/08/22
[Qemu-devel] [PATCH 4/5] trace-cmd: Add non-blocking option for open() and splice_read(), Yoshihiro YUNOMAE, 2012/08/22
[Qemu-devel] [PATCH 5/5] trace-cmd: Use polling function, Yoshihiro YUNOMAE, 2012/08/22