Messages in this thread Patch in this message | | | From | Eric Dumazet <> | Date | Thu, 7 Oct 2021 15:13:46 -0700 | Subject | Re: [PATCH] x86/apic: reduce cache line misses in __x2apic_send_IPI_mask() |
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On Thu, Oct 7, 2021 at 7:13 AM Eric Dumazet <edumazet@google.com> wrote: > > On Thu, Oct 7, 2021 at 7:07 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Thu, Oct 07, 2021 at 07:04:09AM -0700, Eric Dumazet wrote: > > > Good idea, I will try this. > > > Hopefully nr_cpu_ids is populated there ? > > > > Lets hope :-), I'm always terminally lost in early bringup. I figure it > > should be painfully obvious if it goes wrong. > > The answer seems to be yes on hosts I tested.
I have one more question about __x2apic_send_IPI_mask()
Would it make sense to disable hard irqs in __x2apic_send_IPI_mask() only for CONFIG_CPUMASK_OFFSTACK=y builds ?
It seems wasteful to use tiny per-cpu variables and block hard irqs.
Quick and very dirty patch :
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c index e696e22d0531976f7cba72ed17443592eac72c13..c5076d40d4ea7bc9ffb06728531d91777a32cef4 100644 --- a/arch/x86/kernel/apic/x2apic_cluster.c +++ b/arch/x86/kernel/apic/x2apic_cluster.c @@ -44,15 +44,18 @@ static void __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest) { unsigned int cpu, clustercpu; - struct cpumask *tmpmsk; + cpumask_var_t tmpmsk; +#ifdef CONFIG_CPUMASK_OFFSTACK unsigned long flags; +#endif u32 dest;
/* x2apic MSRs are special and need a special fence: */ weak_wrmsr_fence(); +#ifdef CONFIG_CPUMASK_OFFSTACK local_irq_save(flags); - tmpmsk = this_cpu_cpumask_var_ptr(ipi_mask); +#endif cpumask_copy(tmpmsk, mask); /* If IPI should not be sent to self, clear current CPU */ if (apic_dest != APIC_DEST_ALLINC) @@ -74,7 +77,9 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest) cpumask_andnot(tmpmsk, tmpmsk, &cmsk->mask); }
+#ifdef CONFIG_CPUMASK_OFFSTACK local_irq_restore(flags); +#endif }
static void x2apic_send_IPI_mask(const struct cpumask *mask, int vector)
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