Re: [Xen-devel] [PATCH v2 04/14] x86/time.c: Use correct guest TSC frequency in tsc_get_info()

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

On 12/07/15 12:53, Boris Ostrovsky wrote:
> On 12/06/2015 03:58 PM, Haozhong Zhang wrote:
> >When the TSC mode of a HVM container is TSC_MODE_DEFAULT or
> >TSC_MODE_PVRDTSCP and no TSC emulation is used, the existing
> >tsc_get_info() uses the host TSC frequency (cpu_khz) as the guest TSC
> >frequency. However, tsc_set_info() may set the guest TSC frequency to a
> >value different than the host. In order to keep consistent to
> >tsc_set_info(), this patch makes tsc_get_info() use the value set by
> >tsc_set_info() as the guest TSC frequency.
> >
> >Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
> >---
> >  xen/arch/x86/time.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> >
> >diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
> >index 1091e69..95df4f1 100644
> >--- a/xen/arch/x86/time.c
> >+++ b/xen/arch/x86/time.c
> >@@ -1749,6 +1749,9 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
> >                    uint64_t *elapsed_nsec, uint32_t *gtsc_khz,
> >                    uint32_t *incarnation)
> >  {
> >+    bool_t enable_tsc_scaling = has_hvm_container_domain(d) &&
> >+                                cpu_has_tsc_ratio;
> 
> && !d->arch.vtsc ?
> 
> (assuming my comment to the previous patch is correct).
>

enable_tsc_scaling in tsc_get_info() is always used in the condition
!d->arch.vtsc, so it's not necessary to include it again in
enable_tsc_scaling.

> 
> >+
> >      *incarnation = d->arch.incarnation;
> >      *tsc_mode = d->arch.tsc_mode;
> >@@ -1769,7 +1772,7 @@ void tsc_get_info(struct domain *d, uint32_t *tsc_mode,
> >          }
> >          tsc = rdtsc();
> >          *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns);
> >-        *gtsc_khz = cpu_khz;
> >+        *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz : cpu_khz;
> >          break;
> >      case TSC_MODE_PVRDTSCP:
> >          if ( d->arch.vtsc )
> >@@ -1779,10 +1782,13 @@ void tsc_get_info(struct domain *d, uint32_t 
> >*tsc_mode,
> >          }
> >          else
> >          {
> >+            struct time_scale *scale = enable_tsc_scaling ?
> >+                                       &this_cpu(cpu_time).tsc_scale :
> >+                                       &d->arch.vtsc_to_ns;
> 
> IIUIC tsc_scale is host property and so why would it be used if TSC scaling
> is available to guests?
>

scale is used below to convert a host TSC to nanosec. When TSC scaling is used,
d->arch.vtsc_to_ns may not base on the host TSC frequency, so I turn to the host
tsc_scale instead.

Haozhong

> -boris
> 
> 
> >              tsc = rdtsc();
> >-            *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns) -
> >+            *elapsed_nsec = scale_delta(tsc, scale) -
> >                              d->arch.vtsc_offset;
> >-            *gtsc_khz = 0; /* ignored by tsc_set_info */
> >+            *gtsc_khz = enable_tsc_scaling ? d->arch.tsc_khz : 0;
> >          }
> >          break;
> >      }
> 

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