Messages in this thread | | | Date | Wed, 9 Jul 2014 15:46:24 +0900 | From | Yasuaki Ishimatsu <> | Subject | Re: [PATCH] x86,cpu-hotplug: clear llc_shared_mask at CPU hotplug |
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Hi Borislav,
Sorry for late reply and thank you for your explanation. I'm implementing your suggestion. After finishing test, I'll post a patch again. So when I post a patch, please review it.
Thanks, Yasuaki Ishimatsu
(2014/07/04 19:59), Borislav Petkov wrote: > On Fri, Jul 04, 2014 at 09:14:57AM +0900, Yasuaki Ishimatsu wrote: >> If so, why following maps are cleared by CPU offline? >> - cpu_sigling_map >> - cpu_core_map > > I'll let you figure that out on your own by doing some quality code > staring. Hint: search for usages outside of the CPU hotplug path. > > In any case, let me try to explain it to you one more time: if the core > numbers are static and don't change across physical hotplug, the cores > which share last level cache also remain the same. This is a static > property which doesn't simply change. > > For example, if cores 6-11 and 34-41 have been sharing the last level > cache, then if the node containing them gets unplugged and replugged > back again - then the same cores share that exact same cache and nothing > has changed. > > Except the core numbers, as you've shown. Which would be not only a > problem for the llc_shared_mask but also a big annoyance for sysadmins > and users having to realize that the topology enumeration has changed > and trying to make sense of what node went where and why isn't it the > same as when the machine booted. > > So what I'm trying to say is, we should keep the core numbering stable > across hotplug to avoid unnecessary confusion; the llc_shared_mask is > just a small issue which results from not doing that. >
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