Messages in this thread | | | Date | Tue, 15 Feb 2011 04:22:59 +0100 | From | Ingo Molnar <> | Subject | Re: [RFC 1/2 -tip/master] x86, x2apic: minimize IPI register writes using cluster groups |
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* Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> 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?
Is there no GFP_NOFAIL or GFP_FAIL_ON_PANIC variant that could be used the 'must not fail' property of the boot-time allocation?
Thanks,
Ingo
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