> On Jul 4, 2019, at 8:52 AM, Thomas Gleixner <t...@linutronix.de> wrote: > > 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 <na...@vmware.com> > Signed-off-by: Thomas Gleixner <t...@linutronix.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 */
It does look better and simpler than my solution.