• Mark Langsdorf's avatar
    KVM: SVM: Support Pause Filter in AMD processors · 565d0998
    Mark Langsdorf authored
    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: default avatarMark Langsdorf <mark.langsdorf@amd.com>
    Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
    565d0998
svm.c 75.3 KB