KVM: SVM: Support Pause Filter in AMD processors (565d0998) · Commits · 戴 / test

New AMD processors (Family 0x10 models 8+) support the Pause Filter Feature. This feature creates a new field in the VMCB called Pause Filter Count. If Pause Filter Count is greater than 0 and intercepting PAUSEs is enabled, the processor will increment an internal counter when a PAUSE instruction occurs instead of intercepting. When the internal counter reaches the Pause Filter Count value, a PAUSE intercept will occur. This feature can be used to detect contended spinlocks, especially when the lock holding VCPU is not scheduled. Rescheduling another VCPU prevents the VCPU seeking the lock from wasting its quantum by spinning idly. Experimental results show that most spinlocks are held for less than 1000 PAUSE cycles or more than a few thousand. Default the Pause Filter Counter to 3000 to detect the contended spinlocks. Processor support for this feature is indicated by a CPUID bit. On a 24 core system running 4 guests each with 16 VCPUs, this patch improved overall performance of each guest's 32 job kernbench by approximately 3-5% when combined with a scheduler algorithm thati caused the VCPU to sleep for a brief period. Further performance improvement may be possible with a more sophisticated yield algorithm. Signed-off-by:

Mark Langsdorf <mark.langsdorf@amd.com> Signed-off-by:

Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/svm.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -57,7 +57,8 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
		u16 intercept_dr_write;
		u32 intercept_exceptions;
		u64 intercept;
		u8 reserved_1[44];
		u8 reserved_1[42];
		u16 pause_filter_count;
		u64 iopm_base_pa;
		u64 msrpm_base_pa;
		u64 tsc_offset;

arch/x86/kvm/svm.c

+13 −0

Original line number	Diff line number	Diff line
		@@ -46,6 +46,7 @@ MODULE_LICENSE("GPL");
		#define SVM_FEATURE_NPT (1 << 0)
		#define SVM_FEATURE_LBRV (1 << 1)
		#define SVM_FEATURE_SVML (1 << 2)
		#define SVM_FEATURE_PAUSE_FILTER (1 << 10)

		#define NESTED_EXIT_HOST 0 /* Exit handled on host level */
		#define NESTED_EXIT_DONE 1 /* Exit caused nested vmexit */
		@@ -654,6 +655,11 @@ static void init_vmcb(struct vcpu_svm *svm)
		svm->nested.vmcb = 0;
		svm->vcpu.arch.hflags = 0;

		if (svm_has(SVM_FEATURE_PAUSE_FILTER)) {
		control->pause_filter_count = 3000;
		control->intercept \|= (1ULL << INTERCEPT_PAUSE);
		}

		enable_gif(svm);
		}

		@@ -2281,6 +2287,12 @@ static int interrupt_window_interception(struct vcpu_svm *svm)
		return 1;
		}

		static int pause_interception(struct vcpu_svm *svm)
		{
		kvm_vcpu_on_spin(&(svm->vcpu));
		return 1;
		}

		static int (svm_exit_handlers[])(struct vcpu_svm svm) = {
		[SVM_EXIT_READ_CR0] = emulate_on_interception,
		[SVM_EXIT_READ_CR3] = emulate_on_interception,
		@@ -2316,6 +2328,7 @@ static int (svm_exit_handlers[])(struct vcpu_svm svm) = {
		[SVM_EXIT_CPUID] = cpuid_interception,
		[SVM_EXIT_IRET] = iret_interception,
		[SVM_EXIT_INVD] = emulate_on_interception,
		[SVM_EXIT_PAUSE] = pause_interception,
		[SVM_EXIT_HLT] = halt_interception,
		[SVM_EXIT_INVLPG] = invlpg_interception,
		[SVM_EXIT_INVLPGA] = invlpga_interception,

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