On Wed, Jul 10, 2013 at 10:46:47AM -0700, Ben Widawsky wrote: > On Wed, Jul 10, 2013 at 06:40:02PM +0100, Chris Wilson wrote: > > 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 > > > the purpose of this is, but it's something you can't fake in userspace. > > > > In fact, isn't this functionality already part of arch/x86, and isn't the > > value already exposed via /proc/cpuinfo? > > -Chris > > > > -- > > Chris Wilson, Intel Open Source Technology Centre > > > Yes to the /proc/cpuinfo bit (I said that). If the implication is just > to use that code, I did a quick search and couldn't find it. I can go > back and check again. Assuming it's externally exposed to drivers, I > would rather use that. > > We still need the HAS_LLC check to differentiate the L3 though. You have to be careful about repurposing PARAM_HAS_LLC though. At the moment it has a dual meaning that the kernel/gpu supports LLC and that we default to placing objects in LLC. If you must expose cache_size through a param, make it a new one and make it explicit. I would also rather just use a param than parse /proc/cpuinfo (especially as some paranoid setups prevent access to /proc/cpuinfo). But we really should not be calling cpuid from our driver, that just looks very very ugly, and given cpuid's history will be a maintenance burden. -Chris -- Chris Wilson, Intel Open Source Technology Centre
