linux-kernel - Re: [PATCH v3 1/5] perf_event: introduce 'inject' event and get HZ

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Message-ID: <20091230094417.GC18190@elte.hu>
Date:	Wed, 30 Dec 2009 10:44:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/5] perf_event: introduce 'inject' event and get HZ


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, 2009-12-30 at 10:28 +0100, Ingo Molnar wrote:
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Tue, 2009-12-29 at 13:21 +0800, Xiao Guangrong wrote:
> > > > 'inject' event is a very useful feature and it's suggested by Ingo
> > > > [ See http://lkml.org/lkml/2009/12/28/31 ]
> > > 
> > > I really dislike the name, event injection to me would be like a write() 
> > > interface where you provide the actual event data to be stuffed in the 
> > > output stream.
> > > 
> > > This just seems like a very weird way of getting data out. A kind of like 
> > > sysconf() but done very strange.
> > 
> > What kind of API would you suggest?
> 
> sysconf() seems ideal for getting single, mostly constant variables out
> of the kernel, we already have non POSIX (read Linux specific) names in
> there.
> 
> _SC_KERNEL_RELOCATION_OFFSET
> _SC_KERNEL_HZ
> 
> or somethings like that comes to mind.

Nah. HZ might be static here but we'll have more dynamic parameters so the 
sysconf API is rather inflexible there.

I was thinking of something that fits into existing perf API schemes, to keep 
it simple and self-sufficient, and to allow for extensions/etc.

	Ingo
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