Re: [Xen-devel] [PATCH v2 07/14] svm: Remove redundant TSC scaling in svm_set_tsc_offset()

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 12/07/15 13:25, Boris Ostrovsky wrote:
> On 12/06/2015 03:58 PM, Haozhong Zhang wrote:
> >Now every caller passes an already scaled offset to
> >svm_set_tsc_offset(), so it's not necessary to recalculate a scaled TSC
> >offset in svm_set_tsc_offset().
> >
> >Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> >---
> >  xen/arch/x86/hvm/svm/svm.c | 15 ++-------------
> >  1 file changed, 2 insertions(+), 13 deletions(-)
> >
> >diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> >index 9d5f2c3..3d22dfa 100644
> >--- a/xen/arch/x86/hvm/svm/svm.c
> >+++ b/xen/arch/x86/hvm/svm/svm.c
> >@@ -826,19 +826,7 @@ static void svm_set_tsc_offset(struct vcpu *v, u64 
> >offset, u64 at_tsc)
> >      struct vmcb_struct *n1vmcb, *n2vmcb;
> >      uint64_t n2_tsc_offset = 0;
> >      struct domain *d = v->domain;
> >-    uint64_t host_tsc, guest_tsc;
> >-
> >-    guest_tsc = hvm_get_guest_tsc_fixed(v, at_tsc);
> >-
> >-    /* Re-adjust the offset value when TSC_RATIO is available */
> >-    if ( cpu_has_tsc_ratio && !d->arch.vtsc )
> >-    {
> >-        if ( at_tsc )
> >-            host_tsc = at_tsc;
> >-        else
> >-            host_tsc = rdtsc();
> >-        offset = svm_get_tsc_offset(host_tsc, guest_tsc, vcpu_tsc_ratio(v));
> >-    }
> >+    uint64_t guest_tsc;
> 
> You could declare it at the first use site below.
>

will move to the first use site.

Haozhong

> Other than that,
> 
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> 
> >      if ( !nestedhvm_enabled(d) ) {
> >          vmcb_set_tsc_offset(vmcb, offset);
> >@@ -854,6 +842,7 @@ static void svm_set_tsc_offset(struct vcpu *v, u64 
> >offset, u64 at_tsc)
> >          n2_tsc_offset = vmcb_get_tsc_offset(n2vmcb) -
> >              vmcb_get_tsc_offset(n1vmcb);
> >          if ( svm->ns_tscratio != DEFAULT_TSC_RATIO ) {
> >+            guest_tsc = hvm_get_guest_tsc_fixed(v, at_tsc);
> >              n2_tsc_offset = svm_get_tsc_offset(guest_tsc,
> >                  guest_tsc + n2_tsc_offset, svm->ns_tscratio);
> >          }
> 

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