Force apicv_update_lock and apicv_nr_irq_window_req to reside in their own cacheline to avoid generating significant contention due to false sharing when KVM is contantly creating IRQ windows. E.g. apicv_inhibit_reasons is read on every VM-Enter; disabled_exits is read on page faults, on PAUSE exits, if a vCPU is scheduled out, etc.; kvmclock_offset is read every time a vCPU needs to refresh kvmclock, and so on and so forth. Isolating the write-mostly fields from all other (read-mostly) fields improves performance by 7-8% when running netperf TCP_RR between two guests on the same physical host when using an in-kernel PIT in re-inject mode. Reported-by: Naveen N Rao (AMD) Closes: https://lore.kernel.org/all/yrxhngndj37edud6tj5y3vunaf7nirwor4n63yf4275wdocnd3@c77ujgialc6r Tested-by: Naveen N Rao (AMD) Signed-off-by: Sean Christopherson --- arch/x86/include/asm/kvm_host.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index b08baeff98b2..8a9f797b6a68 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1435,13 +1435,23 @@ struct kvm_arch { bool apic_access_memslot_enabled; bool apic_access_memslot_inhibited; + /* + * Force apicv_update_lock and apicv_nr_irq_window_req to reside in a + * dedicated cacheline. They are write-mostly, whereas most everything + * else in kvm_arch is read-mostly. Note that apicv_inhibit_reasons is + * read-mostly: toggling VM-wide inhibits is rare; _checking_ for + * inhibits is common. + */ + ____cacheline_aligned /* * Protects apicv_inhibit_reasons and apicv_nr_irq_window_req (with an * asterisk, see kvm_inc_or_dec_irq_window_inhibit() for details). */ struct rw_semaphore apicv_update_lock; - unsigned long apicv_inhibit_reasons; atomic_t apicv_nr_irq_window_req; + ____cacheline_aligned + + unsigned long apicv_inhibit_reasons; gpa_t wall_clock; -- 2.52.0.457.g6b5491de43-goog