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    SubjectRe: [PATCH][KVM][retry 1] Add support for Pause Filtering to AMD SVM
    (copying Ingo)

    Mark Langsdorf wrote:
    > commit 01813db8627e74018c8cec90df7e345839351f23
    > Author: root <root@xendinar01.amd.com>
    > Date: Thu May 7 09:44:10 2009 -0500
    >
    > New AMD processors will 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 1%. Further performance
    > improvement may be possible with a more sophisticated
    > yield algorithm.
    >
    > -Mark Langsdorf
    > Operating System Research Center
    > AMD
    >
    > Signed-off-by: Mark Langsdorf <mark.langsdorf@amd.com>
    >

    (please use git format-patch rather than git show, and set up user.name
    and user.email properly)

    >
    > svm->nested_vmcb = 0;
    > svm->vcpu.arch.hflags = HF_GIF_MASK;
    > +
    > + if (svm_has(SVM_FEATURE_PAUSE_FILTER)) {
    > + control->pause_filter_count = 5000;
    > + control->intercept |= (1ULL << INTERCEPT_PAUSE);
    > + }
    > +
    > }

    3000 or 5000?

    >
    > +static int pause_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
    > +{
    > + /* Simple yield */
    > + vcpu_put(&svm->vcpu);
    > + schedule();
    > + vcpu_load(&svm->vcpu);
    > + return 1;
    > +

    Ingo, will this do anything under CFS, or will CFS note that nothing has
    changed in the accounting and reschedule us immediately?



    --
    error compiling committee.c: too many arguments to function



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