linux-kernel - Re: [RFC GIT PULL] perf/trace/lock optimization/scalability improvements

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Message-ID: <1265562627.12224.99.camel@laptop>
Date:	Sun, 07 Feb 2010 18:10:27 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Mackerras <paulus@...ba.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [RFC GIT PULL] perf/trace/lock optimization/scalability
 improvements

On Wed, 2010-02-03 at 23:07 +0100, Frederic Weisbecker wrote:
> 
> > 
> > Which brings us to the ioctl() interface, we can do the above using
> > ioctl()s, but it seems to me we're starting to get ioctl() heavy and
> > should be looking at alternative ways of extending this.
> > 
> > Anybody any bright ideas?
> > 
> 
> 
> Using ioctl, we can basically have such structure:
> 
> struct perf_inject_req {
>         int start; (in)
>         int len;   (in)
>         int *read;  (out)
> };
> 
> Using an idx will often imply rewalk a whole object list from
> the beginning, which is perfectly fine.
> 
> If you prefer an alternate syscall, I can make it. I've been
> told about ioctl drawbacks by the past, I personally think
> ioctl has not only drawbacks: it avoids a proliferation
> of syscalls. But that's how you prefer.

One thing we could do is add a PERF_TYPE_COLLECTION and have its read()
method do something else than regular counters would, that way we can
use read()/lseek()/stat() fd interface. The only trouble with that is
that doesn't use the 'regular' output buffer.

/me goes try and come up with yet another solution..

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