@@ -1313,9 +1313,17 @@ deprecated. Options are:
=item B<"default">
-Guest rdtsc/p executed natively when monotonicity can be guaranteed
+Guest rdtsc/p is executed natively when monotonicity can be guaranteed
and emulated otherwise (with frequency scaled if necessary).
+If a HVM container in B<default> TSC mode is created on a host that
+provides constant host TSC, its guest TSC frequency will be the same
+as the host. If it is later migrated to another host that provide
+constant host TSC and supports Intel VMX TSC scaling/AMD SVM TSC
+ratio, its guest TSC frequency will be the same before and after
+migration, and guest rdtsc/p will be executed natively as well after
+migration.
+
=item B<"always_emulate">
Guest rdtsc/p always emulated at 1GHz (kernel and user). Guest rdtsc/p
@@ -1337,6 +1345,10 @@ determine when a restore/migration has occurred and assumes guest
obtains/uses pvclock-like mechanism to adjust for monotonicity and
frequency changes.
+If a HVM container in B<native_paravirt> TSC mode can execute both guest
+rdtsc and guest rdtscp natively, then the guest TSC frequency will be
+determined in the similar way to that of B<default> TSC mode.
+
=back
Please see F<docs/misc/tscmode.txt> for more information on this option.
@@ -297,3 +297,24 @@ and also much faster than nearly all OS-provided time mechanisms.
While pvrtscp is too complex for most apps, certain enterprise
TSC-sensitive high-TSC-frequency apps may find it useful to
obtain a significant performance gain.
+
+Hardware TSC Scaling
+
+Intel VMX TSC scaling and AMD SVM TSC ratio allow the guest TSC read
+by guest rdtsc/p increasing in a different frequency than the host
+TSC frequency.
+
+If a HVM container in default TSC mode (tsc_mode=0) or PVRDTSCP mode
+(tsc_mode=3) is created on a host that provides constant TSC, its
+guest TSC frequency will be the same as the host. If it is later
+migrated to another host that provides constant TSC and supports Intel
+VMX TSC scaling/AMD SVM TSC ratio, its guest TSC frequency will be the
+same before and after migration.
+
+For above HVM container in default TSC mode (tsc_mode=0), if above
+hosts support rdtscp, both guest rdtsc and rdtscp instructions will be
+executed natively before and after migration.
+
+For above HVM container in PVRDTSCP mode (tsc_mode=3), if the
+destination host does not support rdtscp, the guest rdtscp instruction
+will be emulated with the guest TSC frequency.
Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com> --- docs/man/xl.cfg.pod.5 | 14 +++++++++++++- docs/misc/tscmode.txt | 21 +++++++++++++++++++++ 2 files changed, 34 insertions(+), 1 deletion(-)