Re: [PATCH][KVM][retry 1] Add support for Pause Filtering to AMD SVM

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(copying Ingo)

Mark Langsdorf wrote:
commit 01813db8627e74018c8cec90df7e345839351f23
Author: root <root@xxxxxxxxxxxxxxxxxx>
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@xxxxxxx>

(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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