[Xen-devel] [PATCH v2 14/14] docs: Add descriptions of TSC scaling in xl.cfg and tscmode.txt

[Haozhong Zhang <haozhong.zhang@xxxxxxxxx>]

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
 docs/man/xl.cfg.pod.5 | 15 ++++++++++++++-
 docs/misc/tscmode.txt | 14 ++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index 2aca8dd..7e19a9b 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -1313,9 +1313,18 @@ 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 not migrated from other hosts
+and the host TSC monotonicity can be guaranteed, the guest and host TSC
+frequencies will be the same.
+
+If a HVM container in B<default> TSC mode is migrated to a host that can
+guarantee the TSC monotonicity and supports Intel VMX TSC scaling/AMD SVM
+TSC ratio, guest rdtsc/p will still execute natively after migration and the
+guest TSC frequencies before and after migration will be the same.
+
 =item B<"always_emulate">
 
 Guest rdtsc/p always emulated at 1GHz (kernel and user). Guest rdtsc/p
@@ -1337,6 +1346,10 @@ 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.
diff --git a/docs/misc/tscmode.txt b/docs/misc/tscmode.txt
index e8c84e8..f3b70be 100644
--- a/docs/misc/tscmode.txt
+++ b/docs/misc/tscmode.txt
@@ -297,3 +297,17 @@ 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 the different frequency than the host
+TSC frequency.
+
+For a HVM container is in default TSC mode (tsc_mode=0) or PVRDTSCP
+mode (tsc_mode=3) and can execute both guest rdtsc and rdtscp
+natively, if it is not migrated from other hosts, the guest and host
+TSC frequencies will be the same. If it is migrated to a host
+supporting Intel VMX TSC scaling/AMD SVM TSC ratio and can still
+execute guest rdtsc and rdtscp natively, the guest TSC frequencies
+before and after migration will be the same.
-- 
2.6.3


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