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SubjectRe: [RFCv3 0/9] perf tool: parser generator for events parsing
On Wed, Jan 25, 2012 at 11:49:33AM +0100, Peter Zijlstra wrote:
> On Tue, 2012-01-24 at 16:53 -0800, Greg KH wrote:
>
> > Well, what's to keep someone from exploding one of those files to go
> > over the buffer size without knowing it?
>
> The content is known at compile time, we could put checks in. But yeah
> 4k isn't that much text..
>
> > 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?
>
> Ah, yeah, documentation, wasn't that written in C :-)
>
> But fair enough... Anyway, the purpose is to describe the magic bits
> that go into perf_event_attr::config[012] for a particular pmu.
>
> Basically they're the 'hardware' bitmasks we want to export, so that
> userspace can deal with sane name/value pairs.
>
> > 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.
>
> The whole purpose was to drive a parser :-) Anyway, is:
> "config:0-7,32-35" acceptable for a single file?
>
> This means, the 'config' member of struct perf_event_attr bits 0-7,32-35
> form a bitfield whose name is then given by the filename that has this
> content.

Yes, that would be fine.

> > So yes, multiple sysfs files do make sense, the resource load should be
> > almost non-existant for new ones.
>
> Surely all these attribute objects take more space than a few lines of
> text, but ok, I guess multiple files it is.

Great, thanks for asking.

greg k-h


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