linux-kernel - Re: [RFCv3 0/9] perf tool: parser generator for events parsing

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Message-ID: <20120125005342.GA24662@kroah.com>
Date:	Tue, 24 Jan 2012 16:53:42 -0800
From:	Greg KH <greg@...ah.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Jiri Olsa <jolsa@...hat.com>, acme@...hat.com, mingo@...e.hu,
	paulus@...ba.org, cjashfor@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFCv3 0/9] perf tool: parser generator for events parsing

On Tue, Jan 24, 2012 at 05:26:04PM +0100, Peter Zijlstra wrote:
> On Mon, 2012-01-16 at 13:31 +0100, Jiri Olsa wrote:
> > Here's new version of event parsing patchset. To summarize:
> >  - adding event parser bison/flex generator
> >  - the event syntax stays as it was
> >  - adding event format file sysfs attribute
> >    for pmu device
> 
> Added Greg to CC, please also see: https://lkml.org/lkml/2012/1/16/148
> 
> Right, lets hope we can convince the sysfs people that a few lines are
> ok.. if not we need to find another way to represent all this muck, one
> alternative is exploding the whole thing into a sysfs hierarchy like:
> 
> 
> format/event: config:0-7
> ...
> 
> format/config: config:0-63
> format/config1: config1:0-63
> format/config2: config2:0-63
> 
> that will of course consume loads more resources but if that's what it
> takes :-(

Well, what's to keep someone from exploding one of those files to go
over the buffer size without knowing it?

Even after reading the above link, I can't really understand what this
is being used for.  As it's sysfs files, why aren't Documentation/ABI/
files also being created with the patch explaining it all?

Again, if at all possible, sysfs should be one value per file.  Please
NEVER create a sysfs file that requires a parser to determine what is
going on in it.  It should be a simple 'read the value' type thing.

So yes, multiple sysfs files do make sense, the resource load should be
almost non-existant for new ones.

thanks,

greg k-h
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