Messages in this thread Patch in this message | | | From | Eric Dumazet <> | Date | Wed, 13 Oct 2021 11:02:46 -0700 | Subject | Re: [PATCH] x86/apic: reduce cache line misses in __x2apic_send_IPI_mask() |
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On Tue, Oct 12, 2021 at 5:46 AM Peter Zijlstra <peterz@infradead.org> wrote:
> I'm really conflicted about this. On the one hand, yes absolutely. On > the other hand, urgh, code ugly :-)
That was indeed some ugly hack.
I cooked this more generic patch instead, I am currently testing it. (generic as : we no longer disable hard irqs, regardless of some CONFIG option )
diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c index e696e22d0531976f7cba72ed17443592eac72c13..7ad81467ce33349dee1ceaf0cefc8375d60213f6 100644 --- a/arch/x86/kernel/apic/x2apic_cluster.c +++ b/arch/x86/kernel/apic/x2apic_cluster.c @@ -22,7 +22,10 @@ struct cluster_mask { */ static u32 *x86_cpu_to_logical_apicid __read_mostly;
-static DEFINE_PER_CPU(cpumask_var_t, ipi_mask); +#define IPI_NEST_MAX 3 +static DEFINE_PER_CPU(cpumask_var_t, ipi_mask[IPI_NEST_MAX]); +static DEFINE_PER_CPU(int, ipi_nest_level); + static DEFINE_PER_CPU_READ_MOSTLY(struct cluster_mask *, cluster_masks); static struct cluster_mask *cluster_hotplug_mask;
@@ -45,14 +48,18 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest) { unsigned int cpu, clustercpu; struct cpumask *tmpmsk; - unsigned long flags; + int nest_level; u32 dest;
/* x2apic MSRs are special and need a special fence: */ weak_wrmsr_fence(); - local_irq_save(flags);
- tmpmsk = this_cpu_cpumask_var_ptr(ipi_mask); + preempt_disable(); + nest_level = this_cpu_inc_return(ipi_nest_level) - 1; + if (WARN_ON_ONCE(nest_level >= IPI_NEST_MAX)) + goto end; + + tmpmsk = this_cpu_cpumask_var_ptr(ipi_mask[nest_level]); cpumask_copy(tmpmsk, mask); /* If IPI should not be sent to self, clear current CPU */ if (apic_dest != APIC_DEST_ALLINC) @@ -74,7 +81,9 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest) cpumask_andnot(tmpmsk, tmpmsk, &cmsk->mask); }
- local_irq_restore(flags); +end: + this_cpu_dec(ipi_nest_level); + preempt_enable(); }
static void x2apic_send_IPI_mask(const struct cpumask *mask, int vector) @@ -153,20 +162,26 @@ static int alloc_clustermask(unsigned int cpu, int node)
static int x2apic_prepare_cpu(unsigned int cpu) { + int i; + if (alloc_clustermask(cpu, cpu_to_node(cpu)) < 0) return -ENOMEM; - if (!zalloc_cpumask_var(&per_cpu(ipi_mask, cpu), GFP_KERNEL)) - return -ENOMEM; + for (i = 0 ; i < IPI_NEST_MAX; i++) { + if (!zalloc_cpumask_var(&per_cpu(ipi_mask[i], cpu), GFP_KERNEL)) + return -ENOMEM; + } return 0; }
static int x2apic_dead_cpu(unsigned int dead_cpu) { struct cluster_mask *cmsk = per_cpu(cluster_masks, dead_cpu); + int i;
if (cmsk) cpumask_clear_cpu(dead_cpu, &cmsk->mask); - free_cpumask_var(per_cpu(ipi_mask, dead_cpu)); + for (i = 0; i < IPI_NEST_MAX; i++) + free_cpumask_var(per_cpu(ipi_mask[i], dead_cpu)); return 0; }
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