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

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

(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:

quoted

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).

-- Steve