Commit 832df3d4 authored Jul 22, 2019 by Thomas Gleixner

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@vmware.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20190722105220.768238809@linutronix.de

parent d0a7166b

arch/x86/kernel/apic/ipi.c

+11 −13

Original line number	Diff line number	Diff line
		@@ -83,23 +83,21 @@ void native_send_call_func_single_ipi(int cpu)

		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
		sendmask:
		apic->send_IPI_mask(mask, CALL_FUNCTION_VECTOR);

		free_cpumask_var(allbutself);
		}

		#endif /* CONFIG_SMP */

Admin message