Re: [PATCH] drm/i915: Expose LLC size to user space

Ben Widawsky
2013-07-10T17:11:45Z

On Wed, Jul 10, 2013 at 09:40:18AM -0700, Ben Widawsky wrote:
> On Wed, Jul 10, 2013 at 09:59:01AM +0100, Chris Wilson wrote:
> > On Tue, Jul 09, 2013 at 07:58:02PM -0700, Ben Widawsky wrote:
> > > The algorithm/information was originally written by Chad, though I
> > > changed the control flow, and I think his original code had a couple of
> > > bugs, though I didn't look very hard before rewriting. That could have
> > > also been different interpretations of the spec.
> >
> > Just a cpuid query that can already be done more simply from userspace
> > (i.e. with no syscalls)? I was expecting a lot more magic.
> > -Chris
> >
> > --
> > Chris Wilson, Intel Open Source Technology Centre
>
> Chad wrote this originally for mesa. And yes, it's doable from
> userspace. Chatting with Daniel, we thought maybe other GPU clients
> might want this info, and so a central place to put the code would be
> nice, in case there are quirks or anything like that (I've had a
> particularly hard time figuring out if Xeon really has L3 or not).
>
> So what's a central place? Libdrm, everybody uses that right? You can
> read /proc/cpuinfo as far as I know, but then you still need to query
> the HAS_LLC getparam to figure out what kind of L3 (or do your own
> chipset ID check).
>
> In addition to the centrality argument, I noticed while poking around
> cpuid in the kernel that it is a vitalized function. I'm not sure what
That's the last time I let vim tell me I spelled "virtualized" wrong:

cpuid in the kernel that it is a virtualized function
>
> the purpose of this is, but it's something you can't fake in userspace.
>
>
> --
> Ben Widawsky, Intel Open Source Technology Center
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--
Ben Widawsky, Intel Open Source Technology Center