Messages in this thread | | | Date | Mon, 14 Feb 2011 18:10:00 +0300 | From | Cyrill Gorcunov <> | Subject | Re: [RFC 1/2 -tip/master] x86, x2apic: minimize IPI register writes using cluster groups |
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On 02/14/2011 02:45 PM, Ingo Molnar wrote: > > * Cyrill Gorcunov<gorcunov@gmail.com> wrote: > >> In the case of x2apic cluster mode we can group IPI register writes based on the >> cluster group instead of individual per-cpu destiantion messages. This reduces the >> apic register writes and reduces the amount of IPI messages (in the best case we >> can reduce it by a factor of 16). >> >> With this change, microbenchmark measuring the cost of flush_tlb_others(), with >> the flush tlb IPI being sent from a cpu in the socket-1 to all the logical cpus in >> socket-2 (on a Westmere-EX system that has 20 logical cpus in a socket) is 3x >> times better now (compared to the former 'send one-by-one' algorithm). > > Pretty nice! > > I have a few structural and nitpicking comments:
Thanks a lot for review, Ingo! I'll address all the nits during this week.
... > >> +void x2apic_init_cpu_notifier(void) >> +{ >> + int cpu = smp_processor_id(); >> >> + zalloc_cpumask_var(&per_cpu(cpus_in_cluster, cpu), GFP_KERNEL); >> + zalloc_cpumask_var(&per_cpu(ipi_mask, cpu), GFP_KERNEL); >> + BUG_ON(!per_cpu(cpus_in_cluster, cpu) || !per_cpu(ipi_mask, cpu)); > > Such a BUG_ON() is not particularly user friendly - and this could trigger during > CPU hotplug events, i.e. while the system is fully booted up, right? > > Thanks, > > Ingo
Yup is not that much friendly but it's called during system bootup, hotplug events are handled by
+static int __cpuinit +cluster_setup(struct notifier_block *nfb, unsigned long action, void *hcpu) +{ + unsigned int cpu = (unsigned long)hcpu; + int err = 0; + + switch (action) { + case CPU_UP_PREPARE: + zalloc_cpumask_var(&per_cpu(cpus_in_cluster, cpu), GFP_KERNEL); + zalloc_cpumask_var(&per_cpu(ipi_mask, cpu), GFP_KERNEL); + if (!per_cpu(cpus_in_cluster, cpu) || !per_cpu(ipi_mask, cpu)) { + free_cpumask_var(per_cpu(cpus_in_cluster, cpu)); + free_cpumask_var(per_cpu(ipi_mask, cpu)); + err = -ENOMEM; + } + break;
so it returns -ENOMEM if failed. And btw just noted that we forgot to make x2apic_init_cpu_notifier being in __init section.
Or I miss something?
-- Cyrill
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