Messages in this thread |  | | | Date | Fri, 08 May 2009 21:44:22 +0300 | | From | Avi Kivity <> | | Subject | Re: [PATCH][KVM][retry 2] Add support for Pause Filtering to AMD SVM |
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Mark Langsdorf wrote: > From 01813db8627e74018c8cec90df7e345839351f23 Mon Sep 17 00:00:00 2001 > From: Mark Langsdorf <mark.langsdorf@amd.com> > 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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