Messages in this thread | | | Date | Mon, 14 Feb 2022 14:45:49 +0100 | Subject | Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64 | From | Paul Menzel <> |
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Dear David,
Am 29.12.21 um 14:54 schrieb David Woodhouse: > On Wed, 2021-12-29 at 14:18 +0100, Paul Menzel wrote: >>> Or the one in >>> https://lore.kernel.org/lkml/d4cde50b4aab24612823714dfcbe69bc4bb63b60.camel@infradead.org >>> >>> which makes it do nothing except prepare all the CPUs before bringing >>> them up one at a time? >> >> I applied it on top the other one, and it made no difference either. > > It's possible I missed something else in the prepare stage that doesn't > cope with all CPUs being prepared first. > > My next attempt might be to change the loop in bringup_nonboot_cpus() > to bring all the CPUs not to the CPUHP_BP_PARALLEL_DYN state(s) but > instead just bring them to somewhere like CPUHP_RCUTREE_PREP, which is > somewhere in the middle between CPUHP_OFFLINE and CPUHP_BRINGUP_CPU. > > Then a binary chop search — if that one boots, try maybe > CPUHP_TOPOLOGY_PREPARE. And if not, try CPUHP_PROFILE_PREPARE. Etc. > >>> My current theory (not that I've spent that much time thinking about it >>> in the last week) is that there's something about the existing CPU >>> bringup, possibly a CPU bug or something special about the AMD CPUs, >>> which is triggered by just making it a little bit *faster*, which is >>> why bringing them up from kexec (especially in qemu) can cause it too? >> >> Would having the serial console enabled make a difference? > > Yes. I couldn't make this fail in my EC2 m6a instance (for clean boots; > I have never managed to kexec it) until I turned off the serial console > to make things go faster. > >>> Tom seemed to find that it was in load_TR_desc(), so if you could try >>> this hack on a machine that doesn't magically wink out of existence on >>> a triplefault before even flushing its serial output, that would be >>> much appreciated... > >> Unfortunately, no more messages were printed on the serial console. > > I suppose we need to litter those outputs somewhere earlier in the > trampoline then, perhaps it *isn't* getting to load_TR_desc() in your > case? > > Will be back online properly next week and can actually provide some of > the above suggestions in patch form if you're willing to keep testing.
Sorry for replying so late. I saw your v4 patches, and tried commit 5e3524d21d2a () from your branch `parallel-5.17-part1`. Unfortunately, the boot problem still persists on an AMD Ryzen 3 2200 g system, I tested with. Please tell, where I should report these results too (here or posted v4 patches).
Also, do you have (physical) access to a system with an AMD CPU? If not, maybe we can get you one, so it’s more convenient for you to test.
Kind regards,
Paul
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