Mark Langsdorf wrote:
From 01813db8627e74018c8cec90df7e345839351f23 Mon Sep 17 00:00:00 2001
From: Mark Langsdorf <mark.langsdorf@xxxxxxx>
Date: Thu, 7 May 2009 09:44:10 -0500
Subject: [PATCH] Add support for Pause Filtering to AMD SVM
What's the differences wrt retry 1?
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.
3000.
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.
Like I mentioned earlier, I don't think schedule() does anything on CFS.
Try sched_yield(), but set /proc/sys/kernel/sched_compat_yield.
+
+ if (svm_has(SVM_FEATURE_PAUSE_FILTER)) {
+ control->pause_filter_count = 5000;
+ control->intercept |= (1ULL << INTERCEPT_PAUSE);
+ }
+
Here, 5000?
}
static int svm_vcpu_reset(struct kvm_vcpu *vcpu)
@@ -2087,6 +2094,15 @@ static int interrupt_window_interception(struct vcpu_svm *svm,
return 1;
}
+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;
+}
+
You don't need to vcpu_put() and vcpu_load(). The scheduler will call
them for you if/when it switches tasks.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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