linux-kernel - [GIT pull] x86/apic for v5.16-rc1

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Message-ID: <163572865146.3357115.6271807450024716473.tglx@xen13>
Date:   Mon,  1 Nov 2021 02:16:07 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [GIT pull] x86/apic for v5.16-rc1

Linus,

please pull the latest x86/apic branch from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-apic-2021-11-01

up to:  cc95a07fef06: x86/apic: Reduce cache line misses in __x2apic_send_IPI_mask()


x86/apic related update:

  - A single commit which reduces cacheline misses in
    __x2apic_send_IPI_mask() significantly by converting
    x86_cpu_to_logical_apicid() to an array instead of using per CPU
    storage. This reduces the cost for a full broadcast on a dual socket
    system with 256 CPUs from 33 down to 11 microseconds.


Thanks,

	tglx

------------------>
Eric Dumazet (1):
      x86/apic: Reduce cache line misses in __x2apic_send_IPI_mask()


 arch/x86/kernel/apic/x2apic_cluster.c | 27 +++++++++++++++++++++------
 1 file changed, 21 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/apic/x2apic_cluster.c b/arch/x86/kernel/apic/x2apic_cluster.c
index f4da9bb69a88..e696e22d0531 100644
--- a/arch/x86/kernel/apic/x2apic_cluster.c
+++ b/arch/x86/kernel/apic/x2apic_cluster.c
@@ -15,9 +15,15 @@ struct cluster_mask {
 	struct cpumask	mask;
 };
 
-static DEFINE_PER_CPU(u32, x86_cpu_to_logical_apicid);
+/*
+ * __x2apic_send_IPI_mask() possibly needs to read
+ * x86_cpu_to_logical_apicid for all online cpus in a sequential way.
+ * Using per cpu variable would cost one cache line per cpu.
+ */
+static u32 *x86_cpu_to_logical_apicid __read_mostly;
+
 static DEFINE_PER_CPU(cpumask_var_t, ipi_mask);
-static DEFINE_PER_CPU(struct cluster_mask *, cluster_masks);
+static DEFINE_PER_CPU_READ_MOSTLY(struct cluster_mask *, cluster_masks);
 static struct cluster_mask *cluster_hotplug_mask;
 
 static int x2apic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
@@ -27,7 +33,7 @@ static int x2apic_acpi_madt_oem_check(char *oem_id, char *oem_table_id)
 
 static void x2apic_send_IPI(int cpu, int vector)
 {
-	u32 dest = per_cpu(x86_cpu_to_logical_apicid, cpu);
+	u32 dest = x86_cpu_to_logical_apicid[cpu];
 
 	/* x2apic MSRs are special and need a special fence: */
 	weak_wrmsr_fence();
@@ -58,7 +64,7 @@ __x2apic_send_IPI_mask(const struct cpumask *mask, int vector, int apic_dest)
 
 		dest = 0;
 		for_each_cpu_and(clustercpu, tmpmsk, &cmsk->mask)
-			dest |= per_cpu(x86_cpu_to_logical_apicid, clustercpu);
+			dest |= x86_cpu_to_logical_apicid[clustercpu];
 
 		if (!dest)
 			continue;
@@ -94,7 +100,7 @@ static void x2apic_send_IPI_all(int vector)
 
 static u32 x2apic_calc_apicid(unsigned int cpu)
 {
-	return per_cpu(x86_cpu_to_logical_apicid, cpu);
+	return x86_cpu_to_logical_apicid[cpu];
 }
 
 static void init_x2apic_ldr(void)
@@ -103,7 +109,7 @@ static void init_x2apic_ldr(void)
 	u32 cluster, apicid = apic_read(APIC_LDR);
 	unsigned int cpu;
 
-	this_cpu_write(x86_cpu_to_logical_apicid, apicid);
+	x86_cpu_to_logical_apicid[smp_processor_id()] = apicid;
 
 	if (cmsk)
 		goto update;
@@ -166,12 +172,21 @@ static int x2apic_dead_cpu(unsigned int dead_cpu)
 
 static int x2apic_cluster_probe(void)
 {
+	u32 slots;
+
 	if (!x2apic_mode)
 		return 0;
 
+	slots = max_t(u32, L1_CACHE_BYTES/sizeof(u32), nr_cpu_ids);
+	x86_cpu_to_logical_apicid = kcalloc(slots, sizeof(u32), GFP_KERNEL);
+	if (!x86_cpu_to_logical_apicid)
+		return 0;
+
 	if (cpuhp_setup_state(CPUHP_X2APIC_PREPARE, "x86/x2apic:prepare",
 			      x2apic_prepare_cpu, x2apic_dead_cpu) < 0) {
 		pr_err("Failed to register X2APIC_PREPARE\n");
+		kfree(x86_cpu_to_logical_apicid);
+		x86_cpu_to_logical_apicid = NULL;
 		return 0;
 	}
 	init_x2apic_ldr();