Re: Re: [PATCH 2/5] trace-cmd: Use tracing directory to count CPUs

(2012/08/23 18:08), Steven Rostedt wrote:

On Thu, 2012-08-23 at 12:00 +0900, Masami Hiramatsu wrote:

quoted

(2012/08/23 11:01), Masami Hiramatsu wrote:

quoted

(2012/08/22 22:41), Steven Rostedt wrote:

quoted

On Wed, 2012-08-22 at 17:43 +0900, Yoshihiro YUNOMAE wrote:

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From: Masami Hiramatsu <redacted>

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.

quoted

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: masami.hiramatsu.pt@hitachi.com