Messages in this thread | | | Date | Fri, 20 May 2022 16:06:52 +0100 | From | Sudeep Holla <> | Subject | Re: [PATCH v2 8/8] arch_topology: Add support to build llc_sibling on DT platforms |
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On Fri, May 20, 2022 at 09:36:20AM -0500, Rob Herring wrote: > On Fri, May 20, 2022 at 01:59:59PM +0100, Sudeep Holla wrote: > > On Thu, May 19, 2022 at 01:10:51PM -0500, Rob Herring wrote: > > > On Wed, May 18, 2022 at 4:34 AM Sudeep Holla <sudeep.holla@arm.com> wrote: > > > > > > > > ACPI PPTT provides cache identifiers and especially the last level cache > > > > identifier is used in obtaining last level cache siblings amongst CPUs. > > > > > > > > While we have the cpu map representing all the CPUs sharing last level > > > > cache in the cacheinfo driver, it is populated quite late in the boot > > > > while the information is needed to build scheduler domains quite early. > > > > > > Late is because it's a device_initcall() rather than late in the cpu > > > hotplug state machine, right? > > > > Right. The expectation is to run in on each online CPU in CPU hotplug state > > machine for some architectures. We may not need that on arm64 especially > > since we get all info from DT or ACPI, but e.g. x86 uses cpuid which needs > > to be executed on that CPU. > > That's a separate issue. I'm not suggesting changing that part (that > would just be an optimization). > > > > The late aspect is for sysfs presumably,but I think we could decouple that. > > > > OK, not sure when this sched_domain info is actually needed. It think it > > could be decoupled if we can wait until all the cpus are online. > > No need to wait for all cpus to be online. I think you keep doing > it as part of cpu hotplug. The device_initcall() is used because you > cannot have struct device or sysfs calls before the driver core is > initialized. If we run the cacheinfo code earlier (I think the arch code > will have to call it) just like the topology code and skip the sysfs > parts, then you can use it. >
Yes I was thinking something on similar lines, though I didn't think of pushing code to arch. Let me check, must be possible.
> > > Do all the firmware cache parsing early and then populate the sysfs parts > > > later. > > > > Yes that may work on DT/ACPI based systems, as I said x86 relies on cpuid. > > I'd assume using cpuid works at any time? >
I think so, I can't recall the details since I looked at that about 5 years ago. I have to check again anyways to explore early initialisation.
-- Regards, Sudeep
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