[Xen-devel] [PATCH 1/2] x86/svm: add support for pause filtering threshold

[Brian Woods <brian.woods@xxxxxxx>]

Add support for enabling the pause filtering threshold feature.  This
causes the pause filtering count to reset if there's pause filtering
threshold cycles or greater between pauses.  See AMD APM Vol 2 Section
15.14.4 for more details.

The values of the pause filtering count and threshold were found by
iterating over different values of the count and threshold while running
kernbench and a pi spigot algorithm with yields placed in it.  A
balanced setting for both variable provides:

(Using averaged elapsed time with kernbench)
old = 852.0
new = 848.8
improvement = .4%

For system without pause filtering threshold, the change, from 3000 to
4000 for the count, should not negatively effect system performance.

Signed-off-by: Brian Woods <brian.woods@xxxxxxx>
---
 xen/include/asm-x86/hvm/svm/svm.h  | 5 ++++-
 xen/include/asm-x86/hvm/svm/vmcb.h | 3 ++-
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/include/asm-x86/hvm/svm/svm.h 
b/xen/include/asm-x86/hvm/svm/svm.h
index 462cb89b7c..593546fb56 100644
--- a/xen/include/asm-x86/hvm/svm/svm.h
+++ b/xen/include/asm-x86/hvm/svm/svm.h
@@ -64,6 +64,7 @@ extern u32 svm_feature_flags;
 #define SVM_FEATURE_FLUSHBYASID    6 /* TLB flush by ASID support */
 #define SVM_FEATURE_DECODEASSISTS  7 /* Decode assists support */
 #define SVM_FEATURE_PAUSEFILTER   10 /* Pause intercept filter support */
+#define SVM_FEATURE_PAUSETHRESH   12 /* Pause intercept filter support */
 #define SVM_FEATURE_VLOADSAVE     15 /* virtual vmload/vmsave */
 #define SVM_FEATURE_VGIF          16 /* Virtual GIF */
 
@@ -76,10 +77,12 @@ extern u32 svm_feature_flags;
 #define cpu_has_svm_decode    cpu_has_svm_feature(SVM_FEATURE_DECODEASSISTS)
 #define cpu_has_svm_vgif      cpu_has_svm_feature(SVM_FEATURE_VGIF)
 #define cpu_has_pause_filter  cpu_has_svm_feature(SVM_FEATURE_PAUSEFILTER)
+#define cpu_has_pause_thresh  cpu_has_svm_feature(SVM_FEATURE_PAUSETHRESH)
 #define cpu_has_tsc_ratio     cpu_has_svm_feature(SVM_FEATURE_TSCRATEMSR)
 #define cpu_has_svm_vloadsave cpu_has_svm_feature(SVM_FEATURE_VLOADSAVE)
 
-#define SVM_PAUSEFILTER_INIT    3000
+#define SVM_PAUSEFILTER_INIT    4000
+#define SVM_PAUSETHRESH_INIT    1000
 
 /* TSC rate */
 #define DEFAULT_TSC_RATIO       0x0000000100000000ULL
diff --git a/xen/include/asm-x86/hvm/svm/vmcb.h 
b/xen/include/asm-x86/hvm/svm/vmcb.h
index 9d5dfc58f2..de07429dff 100644
--- a/xen/include/asm-x86/hvm/svm/vmcb.h
+++ b/xen/include/asm-x86/hvm/svm/vmcb.h
@@ -412,7 +412,7 @@ struct vmcb_struct {
     u64 res04;                  /* offset 0x28 */
     u64 res05;                  /* offset 0x30 */
     u32 res06;                  /* offset 0x38 */
-    u16 res06a;                 /* offset 0x3C */
+    u16 _pause_filter_thresh;   /* offset 0x3C - cleanbit 0 */
     u16 _pause_filter_count;    /* offset 0x3E - cleanbit 0 */
     u64 _iopm_base_pa;          /* offset 0x40 - cleanbit 1 */
     u64 _msrpm_base_pa;         /* offset 0x48 - cleanbit 1 */
@@ -568,6 +568,7 @@ VMCB_ACCESSORS(exception_intercepts, intercepts)
 VMCB_ACCESSORS(general1_intercepts, intercepts)
 VMCB_ACCESSORS(general2_intercepts, intercepts)
 VMCB_ACCESSORS(pause_filter_count, intercepts)
+VMCB_ACCESSORS(pause_filter_thresh, intercepts)
 VMCB_ACCESSORS(tsc_offset, intercepts)
 VMCB_ACCESSORS(iopm_base_pa, iopm)
 VMCB_ACCESSORS(msrpm_base_pa, iopm)
-- 
2.11.0


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