[v3,01/13] x86/time.c: Use correct guest TSC frequency in tsc_set_info()

Commit Message

Haozhong Zhang Dec. 31, 2015, 3:03 a.m. UTC

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 <[e-mail]>
---
Changes in v3:
 (addressing Boris Ostrovsky's comments)
 * Add the missing ! before d->arch.vtsc when initializing enable_tsc_scaling.
 * Use this_cpu(cpu_time).tsc_scale for both scaling and non-scaling cases.
 * Adapt comments for some TSC-related fields in struct arch_domain.

 xen/arch/x86/time.c          | 9 +++++++--
 xen/include/asm-x86/domain.h | 9 ++++++---
 2 files changed, 13 insertions(+), 5 deletions(-)

Comments

Boris Ostrovsky Jan. 4, 2016, 5:44 p.m. UTC | #1

On 12/30/2015 10:03 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 <[e-mail]>

Reviewed-by: Boris Ostrovsky <[e-mail]>

Patch

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index b5223cf..0059b6a 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 +1876,8 @@  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) -
+            d->arch.vtsc_offset = scale_delta(rdtsc(),
+                                              &this_cpu(cpu_time).tsc_scale) -
                                   elapsed_nsec;
         }
         break;
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index e8f7037..405adef 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -347,9 +347,12 @@  struct arch_domain
     s_time_t vtsc_last;      /* previous TSC value (guarantee monotonicity) */
     spinlock_t vtsc_lock;
     uint64_t vtsc_offset;    /* adjustment for save/restore/migrate */
-    uint32_t tsc_khz;        /* cached khz for certain emulated cases */
-    struct time_scale vtsc_to_ns; /* scaling for certain emulated cases */
-    struct time_scale ns_to_vtsc; /* scaling for certain emulated cases */
+    uint32_t tsc_khz;        /* cached guest khz for certain emulated or
+                                hardware TSC scaling cases */
+    struct time_scale vtsc_to_ns; /* scaling for certain emulated or
+                                     hardware TSC scaling cases */
+    struct time_scale ns_to_vtsc; /* scaling for certain emulated or
+                                     hardware TSC scaling cases */
     uint32_t incarnation;    /* incremented every restore or live migrate
                                 (possibly other cases in the future */
 #if !defined(NDEBUG) || defined(PERF_COUNTERS)