diff options
| author | Sean Christopherson <seanjc@google.com> | 2026-01-24 01:45:14 +0300 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2026-03-03 01:51:36 +0300 |
| commit | fa78a514d632ed2428b7c573108d9658c00d536e (patch) | |
| tree | 333d5677676e7a8189087bc3bd6060e7547e2994 | |
| parent | 5617dddcfa30129562d7028ec766797d8c345f36 (diff) | |
| download | linux-fa78a514d632ed2428b7c573108d9658c00d536e.tar.xz | |
KVM: Isolate apicv_update_lock and apicv_nr_irq_window_req in a cacheline
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) <naveen@kernel.org>
Closes: https://lore.kernel.org/all/yrxhngndj37edud6tj5y3vunaf7nirwor4n63yf4275wdocnd3@c77ujgialc6r
Tested-by: Naveen N Rao (AMD) <naveen@kernel.org>
Link: https://patch.msgid.link/20260123224514.2509129-5-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
| -rw-r--r-- | arch/x86/include/asm/kvm_host.h | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 68db00dc09a0..883b85b3e1de 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1442,12 +1442,22 @@ struct kvm_arch { 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; |