linux-kernel - [patch V2 21/25] x86/smp: Enhance native_send_call_func

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Date:   Thu, 04 Jul 2019 17:52:06 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Nadav Amit <namit@...are.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Feng Tang <feng.tang@...el.com>
Subject: [patch V2 21/25] x86/smp: Enhance native_send_call_func_ipi()

Nadav noticed that the cpumask allocations in native_send_call_func_ipi()
are noticeable in microbenchmarks.

Use the new cpumask_or_equal() function to simplify the decision whether
the supplied target CPU mask is either equal to cpu_online_mask or equal to
cpu_online_mask except for the CPU on which the function is invoked.

cpumask_or_equal() or's the target mask and the cpumask of the current CPU
together and compares it to cpu_online_mask.

If the result is false, use the mask based IPI function, otherwise check
whether the current CPU is set in the target mask and invoke either the
send_IPI_all() or the send_IPI_allbutselt() APIC callback.

Make the shorthand decision also depend on the static key which enables
shorthand mode. That allows to remove the extra cpumask comparison with
cpu_callout_mask.

Reported-by: Nadav Amit <namit@...are.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V2: New patch
---
 arch/x86/kernel/apic/ipi.c |   24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

--- a/arch/x86/kernel/apic/ipi.c
+++ b/arch/x86/kernel/apic/ipi.c
@@ -83,23 +83,21 @@ void native_send_call_func_single_ipi(in

 void native_send_call_func_ipi(const struct cpumask *mask)
 {
-	cpumask_var_t allbutself;
+	if (static_branch_likely(&apic_use_ipi_shorthand)) {
+		unsigned int cpu = smp_processor_id();

-	if (!alloc_cpumask_var(&allbutself, GFP_ATOMIC)) {
-		apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
+		if (!cpumask_or_equal(mask, cpumask_of(cpu), cpu_online_mask))
+			goto sendmask;
+
+		if (cpumask_test_cpu(cpu, mask))
+			apic->send_IPI_all(CALL_FUNCTION_VECTOR);
+		else if (num_online_cpus() > 1)
+			apic->send_IPI_allbutself(CALL_FUNCTION_VECTOR);
 		return;
 	}

-	cpumask_copy(allbutself, cpu_online_mask);
-	cpumask_clear_cpu(smp_processor_id(), allbutself);
-
-	if (cpumask_equal(mask, allbutself) &&
-	    cpumask_equal(cpu_online_mask, cpu_callout_mask))
-		apic->send_IPI_allbutself(CALL_FUNCTION_VECTOR);
-	else
-		apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
-
-	free_cpumask_var(allbutself);
+sendmask:
+	apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
 }

 #endif /* CONFIG_SMP */