Messages in this thread | | | Date | Tue, 20 Sep 2022 14:15:34 +0530 | Subject | Re: [PATCH v3 4/4] arm64: support batched/deferred tlb shootdown during page reclamation | From | Anshuman Khandual <> |
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On 9/20/22 09:09, Barry Song wrote: > On Tue, Sep 20, 2022 at 3:00 PM Anshuman Khandual > <anshuman.khandual@arm.com> wrote: >> >> >> On 8/22/22 13:51, Yicong Yang wrote: >>> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm) >>> +{ >>> + return true; >>> +} >> >> This needs to be conditional on systems, where there will be performance >> improvements, and should not just be enabled all the time on all systems. >> num_online_cpus() > X, which does not hold any cpu hotplug lock would be >> a good metric ? > > for a small system, i don't see how this patch will help, e.g. cpus <= 4; > so we can actually disable tlb-batch on small systems.
Do not subscribe ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH based on NR_CPUS ? That might not help much as the default value is 256 for NR_CPUS.
OR
arch_tlbbatch_should_defer() checks on
1. online cpus (dont enable batched TLB if <= X) 2. ARM64_WORKAROUND_REPEAT_TLBI (dont enable batched TLB)
> just need to check if we will have any race condition since hotplug will > make the condition true and false dynamically.
If should_defer_flush() evaluate to be false, then ptep_clear_flush() clears and flushes the entry right away. This should not race with other queued up TLBI requests, which will be flushed separately. Wondering how there can be a race here !
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