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[Xen-devel] [PATCH] SVM: enables TSC scaling ratio support for SVM
| To: | "'xen-devel@xxxxxxxxxxxxxxxxxxx'" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir@xxxxxxx> |
|---|---|
| Subject: | [Xen-devel] [PATCH] SVM: enables TSC scaling ratio support for SVM |
| From: | Wei Huang <wei.huang2@xxxxxxx> |
| Date: | Fri, 27 May 2011 11:34:59 -0500 |
| Cc: | |
| Delivery-date: | Fri, 27 May 2011 11:31:30 -0700 |
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Future AMD CPUs support TSC scaling. It allows guests to have a
different TSC frequency from host system using this formula: guest_tsc =
host_tsc * tsc_ratio + vmcb_offset. The tsc_ratio is a 64bit MSR
contains a fixed-point number in 8.32 format (8 bits for integer part
and 32bits for fractional part). For instance 0x00000003_80000000 means
tsc_ratio=3.5.
This patch enables TSC scaling ratio for SVM. With it, guest VMs don't need take #VMEXIT to calculate a translated TSC value when it is running under TSC emulation mode. This can SUBSTANTIALLY reduce the rdtsc overhead. Signed-off-by: Wei Huang <wei.huang2@xxxxxxx> arch/x86/hvm/svm/svm.c | 32 +++++++++++++++++++++++++++++++- arch/x86/hvm/svm/vmcb.c | 4 +++- include/asm-x86/hvm/svm/svm.h | 8 ++++++++ include/asm-x86/msr-index.h | 3 +++ 4 files changed, 45 insertions(+), 2 deletions(-)
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