Re: [Xen-devel] [PATCH v2 03/14] x86/time.c: Use correct guest TSC frequency in tsc_set_info()

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 12/07/15 11:57, Boris Ostrovsky wrote:
> On 12/06/2015 03:58 PM, Haozhong Zhang wrote:
> >When TSC_MODE_PVRDTSCP is used for a HVM container and TSC scaling is
> >available, use the non-zero value of argument gtsc_khz of tsc_set_info()
> >as the guest TSC frequency rather than using the host TSC
> >frequency. Otherwise, TSC scaling will not be able get the correct ratio
> >between the host and guest TSC frequencies.
> >
> >Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> >---
> >  xen/arch/x86/time.c | 11 +++++++++--
> >  1 file changed, 9 insertions(+), 2 deletions(-)
> >
> >diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> >index b5223cf..1091e69 100644
> >--- a/xen/arch/x86/time.c
> >+++ b/xen/arch/x86/time.c
> >@@ -1803,6 +1803,8 @@ void tsc_set_info(struct domain *d,
> >                    uint32_t tsc_mode, uint64_t elapsed_nsec,
> >                    uint32_t gtsc_khz, uint32_t incarnation)
> >  {
> >+    bool_t enable_tsc_scaling;
> >+
> >      if ( is_idle_domain(d) || is_hardware_domain(d) )
> >      {
> >          d->arch.vtsc = 0;
> >@@ -1864,7 +1866,9 @@ void tsc_set_info(struct domain *d,
> >      case TSC_MODE_PVRDTSCP:
> >          d->arch.vtsc = !boot_cpu_has(X86_FEATURE_RDTSCP) ||
> >                         !host_tsc_is_safe();
> >-        d->arch.tsc_khz = cpu_khz;
> >+        enable_tsc_scaling = has_hvm_container_domain(d) &&
> >+                             cpu_has_tsc_ratio && d->arch.vtsc;
> >+        d->arch.tsc_khz = (enable_tsc_scaling && gtsc_khz) ? gtsc_khz : 
> >cpu_khz;
> >          set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
> >          d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
> >          if ( d->arch.vtsc )
> >@@ -1872,7 +1876,10 @@ void tsc_set_info(struct domain *d,
> >          else {
> >              /* when using native TSC, offset is nsec relative to power-on
> >               * of physical machine */
> >-            d->arch.vtsc_offset = scale_delta(rdtsc(), &d->arch.vtsc_to_ns) 
> >-
> >+            struct time_scale *scale = enable_tsc_scaling ?
> 
> Do we need this test here? Per previous chunk, enable_tsc_scaling will be
> zero since d->arch.vtsc is false.
> 
> Actually, if you are trying to use (or, rather, account for) TSC scaling,
> shouldn't it be !arch.vtsc there?
>

It really should be !arch.vtsc. Don't know why I missed ! here but my
testing code did not.

Thanks,
Haozhong

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