KVM guest: guest side for eoi avoidance
The idea is simple: there's a bit, per APIC, in guest memory,
that tells the guest that it does not need EOI.
Guest tests it using a single est and clear operation - this is
necessary so that host can detect interrupt nesting - and if set, it can
skip the EOI MSR.
I run a simple microbenchmark to show exit reduction
(note: for testing, need to apply follow-up patch
'kvm: host side for eoi optimization' + a qemu patch
I posted separately, on host):
Before:
Performance counter stats for 'sleep 1s':
47,357 kvm:kvm_entry [99.98%]
0 kvm:kvm_hypercall [99.98%]
0 kvm:kvm_hv_hypercall [99.98%]
5,001 kvm:kvm_pio [99.98%]
0 kvm:kvm_cpuid [99.98%]
22,124 kvm:kvm_apic [99.98%]
49,849 kvm:kvm_exit [99.98%]
21,115 kvm:kvm_inj_virq [99.98%]
0 kvm:kvm_inj_exception [99.98%]
0 kvm:kvm_page_fault [99.98%]
22,937 kvm:kvm_msr [99.98%]
0 kvm:kvm_cr [99.98%]
0 kvm:kvm_pic_set_irq [99.98%]
0 kvm:kvm_apic_ipi [99.98%]
22,207 kvm:kvm_apic_accept_irq [99.98%]
22,421 kvm:kvm_eoi [99.98%]
0 kvm:kvm_pv_eoi [99.99%]
0 kvm:kvm_nested_vmrun [99.99%]
0 kvm:kvm_nested_intercepts [99.99%]
0 kvm:kvm_nested_vmexit [99.99%]
0 kvm:kvm_nested_vmexit_inject [99.99%]
0 kvm:kvm_nested_intr_vmexit [99.99%]
0 kvm:kvm_invlpga [99.99%]
0 kvm:kvm_skinit [99.99%]
57 kvm:kvm_emulate_insn [99.99%]
0 kvm:vcpu_match_mmio [99.99%]
0 kvm:kvm_userspace_exit [99.99%]
2 kvm:kvm_set_irq [99.99%]
2 kvm:kvm_ioapic_set_irq [99.99%]
23,609 kvm:kvm_msi_set_irq [99.99%]
1 kvm:kvm_ack_irq [99.99%]
131 kvm:kvm_mmio [99.99%]
226 kvm:kvm_fpu [100.00%]
0 kvm:kvm_age_page [100.00%]
0 kvm:kvm_try_async_get_page [100.00%]
0 kvm:kvm_async_pf_doublefault [100.00%]
0 kvm:kvm_async_pf_not_present [100.00%]
0 kvm:kvm_async_pf_ready [100.00%]
0 kvm:kvm_async_pf_completed
1.002100578 seconds time elapsed
After:
Performance counter stats for 'sleep 1s':
28,354 kvm:kvm_entry [99.98%]
0 kvm:kvm_hypercall [99.98%]
0 kvm:kvm_hv_hypercall [99.98%]
1,347 kvm:kvm_pio [99.98%]
0 kvm:kvm_cpuid [99.98%]
1,931 kvm:kvm_apic [99.98%]
29,595 kvm:kvm_exit [99.98%]
24,884 kvm:kvm_inj_virq [99.98%]
0 kvm:kvm_inj_exception [99.98%]
0 kvm:kvm_page_fault [99.98%]
1,986 kvm:kvm_msr [99.98%]
0 kvm:kvm_cr [99.98%]
0 kvm:kvm_pic_set_irq [99.98%]
0 kvm:kvm_apic_ipi [99.99%]
25,953 kvm:kvm_apic_accept_irq [99.99%]
26,132 kvm:kvm_eoi [99.99%]
26,593 kvm:kvm_pv_eoi [99.99%]
0 kvm:kvm_nested_vmrun [99.99%]
0 kvm:kvm_nested_intercepts [99.99%]
0 kvm:kvm_nested_vmexit [99.99%]
0 kvm:kvm_nested_vmexit_inject [99.99%]
0 kvm:kvm_nested_intr_vmexit [99.99%]
0 kvm:kvm_invlpga [99.99%]
0 kvm:kvm_skinit [99.99%]
284 kvm:kvm_emulate_insn [99.99%]
68 kvm:vcpu_match_mmio [99.99%]
68 kvm:kvm_userspace_exit [99.99%]
2 kvm:kvm_set_irq [99.99%]
2 kvm:kvm_ioapic_set_irq [99.99%]
28,288 kvm:kvm_msi_set_irq [99.99%]
1 kvm:kvm_ack_irq [99.99%]
131 kvm:kvm_mmio [100.00%]
588 kvm:kvm_fpu [100.00%]
0 kvm:kvm_age_page [100.00%]
0 kvm:kvm_try_async_get_page [100.00%]
0 kvm:kvm_async_pf_doublefault [100.00%]
0 kvm:kvm_async_pf_not_present [100.00%]
0 kvm:kvm_async_pf_ready [100.00%]
0 kvm:kvm_async_pf_completed
1.002039622 seconds time elapsed
We see that # of exits is almost halved.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Michael S. Tsirkin
Avi Kivity
Родитель
8680b94b0e
Коммит
ab9cf4996b
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@ -22,6 +22,7 @@
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#define KVM_FEATURE_CLOCKSOURCE2 3
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#define KVM_FEATURE_ASYNC_PF 4
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#define KVM_FEATURE_STEAL_TIME 5
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#define KVM_FEATURE_PV_EOI 6
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/* The last 8 bits are used to indicate how to interpret the flags field
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* in pvclock structure. If no bits are set, all flags are ignored.
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@ -37,6 +38,7 @@
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#define MSR_KVM_SYSTEM_TIME_NEW 0x4b564d01
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#define MSR_KVM_ASYNC_PF_EN 0x4b564d02
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#define MSR_KVM_STEAL_TIME 0x4b564d03
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#define MSR_KVM_PV_EOI_EN 0x4b564d04
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struct kvm_steal_time {
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__u64 steal;
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@ -89,6 +91,11 @@ struct kvm_vcpu_pv_apf_data {
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__u32 enabled;
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};
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#define KVM_PV_EOI_BIT 0
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#define KVM_PV_EOI_MASK (0x1 << KVM_PV_EOI_BIT)
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#define KVM_PV_EOI_ENABLED KVM_PV_EOI_MASK
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#define KVM_PV_EOI_DISABLED 0x0
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#ifdef __KERNEL__
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#include <asm/processor.h>
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@ -39,6 +39,8 @@
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#include <asm/desc.h>
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#include <asm/tlbflush.h>
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#include <asm/idle.h>
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#include <asm/apic.h>
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#include <asm/apicdef.h>
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static int kvmapf = 1;
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@ -283,6 +285,22 @@ static void kvm_register_steal_time(void)
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cpu, __pa(st));
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}
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static DEFINE_PER_CPU(unsigned long, kvm_apic_eoi) = KVM_PV_EOI_DISABLED;
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static void kvm_guest_apic_eoi_write(u32 reg, u32 val)
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{
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/**
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* This relies on __test_and_clear_bit to modify the memory
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* in a way that is atomic with respect to the local CPU.
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* The hypervisor only accesses this memory from the local CPU so
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* there's no need for lock or memory barriers.
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* An optimization barrier is implied in apic write.
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*/
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if (__test_and_clear_bit(KVM_PV_EOI_BIT, &__get_cpu_var(kvm_apic_eoi)))
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return;
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apic->write(APIC_EOI, APIC_EOI_ACK);
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}
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void __cpuinit kvm_guest_cpu_init(void)
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{
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if (!kvm_para_available())
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@ -300,11 +318,20 @@ void __cpuinit kvm_guest_cpu_init(void)
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smp_processor_id());
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}
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if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
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unsigned long pa;
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/* Size alignment is implied but just to make it explicit. */
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BUILD_BUG_ON(__alignof__(kvm_apic_eoi) < 4);
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__get_cpu_var(kvm_apic_eoi) = 0;
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pa = __pa(&__get_cpu_var(kvm_apic_eoi)) | KVM_MSR_ENABLED;
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wrmsrl(MSR_KVM_PV_EOI_EN, pa);
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}
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if (has_steal_clock)
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kvm_register_steal_time();
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}
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static void kvm_pv_disable_apf(void *unused)
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static void kvm_pv_disable_apf(void)
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{
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if (!__get_cpu_var(apf_reason).enabled)
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return;
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@ -316,11 +343,23 @@ static void kvm_pv_disable_apf(void *unused)
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smp_processor_id());
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}
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static void kvm_pv_guest_cpu_reboot(void *unused)
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{
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/*
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* We disable PV EOI before we load a new kernel by kexec,
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* since MSR_KVM_PV_EOI_EN stores a pointer into old kernel's memory.
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* New kernel can re-enable when it boots.
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*/
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if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
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wrmsrl(MSR_KVM_PV_EOI_EN, 0);
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kvm_pv_disable_apf();
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}
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static int kvm_pv_reboot_notify(struct notifier_block *nb,
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unsigned long code, void *unused)
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{
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if (code == SYS_RESTART)
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on_each_cpu(kvm_pv_disable_apf, NULL, 1);
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on_each_cpu(kvm_pv_guest_cpu_reboot, NULL, 1);
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return NOTIFY_DONE;
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}
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@ -371,7 +410,9 @@ static void __cpuinit kvm_guest_cpu_online(void *dummy)
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static void kvm_guest_cpu_offline(void *dummy)
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{
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kvm_disable_steal_time();
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kvm_pv_disable_apf(NULL);
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if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
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wrmsrl(MSR_KVM_PV_EOI_EN, 0);
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kvm_pv_disable_apf();
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apf_task_wake_all();
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}
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@ -424,6 +465,16 @@ void __init kvm_guest_init(void)
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pv_time_ops.steal_clock = kvm_steal_clock;
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}
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if (kvm_para_has_feature(KVM_FEATURE_PV_EOI)) {
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struct apic **drv;
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for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
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/* Should happen once for each apic */
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WARN_ON((*drv)->eoi_write == kvm_guest_apic_eoi_write);
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(*drv)->eoi_write = kvm_guest_apic_eoi_write;
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}
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}
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#ifdef CONFIG_SMP
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smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;
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register_cpu_notifier(&kvm_cpu_notifier);
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