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[PULL,01/18] qapi: Expand documentation for LostTickPolicy

Message ID 20200215114133.15097-2-armbru@redhat.com
State New
Headers show
Series [PULL,01/18] qapi: Expand documentation for LostTickPolicy | expand

Commit Message

Markus Armbruster Feb. 15, 2020, 11:41 a.m. UTC 
From: Andrea Bolognani <abologna@redhat.com>

The current documentation is fairly terse and not easy to decode
for someone who's not intimately familiar with the inner workings
of timer devices. Expand on it by providing a somewhat verbose
description of what behavior each policy will result in, as seen
from both the guest OS and host point of view.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Message-Id: <20200211183744.210298-1-abologna@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 qapi/misc.json | 28 ++++++++++++++++++++--------
 1 file changed, 20 insertions(+), 8 deletions(-)
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Patch

diff --git a/qapi/misc.json b/qapi/misc.json
index 33b94e3589..cd7445d29f 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -163,17 +163,29 @@ 
 ##
 # @LostTickPolicy:
 #
-# Policy for handling lost ticks in timer devices.
+# Policy for handling lost ticks in timer devices.  Ticks end up getting
+# lost when, for example, the guest is paused.
 #
-# @discard: throw away the missed tick(s) and continue with future injection
-#           normally.  Guest time may be delayed, unless the OS has explicit
-#           handling of lost ticks
+# @discard: throw away the missed ticks and continue with future injection
+#           normally.  The guest OS will see the timer jump ahead by a
+#           potentially quite significant amount all at once, as if the
+#           intervening chunk of time had simply not existed; needless to
+#           say, such a sudden jump can easily confuse a guest OS which is
+#           not specifically prepared to deal with it.  Assuming the guest
+#           OS can deal correctly with the time jump, the time in the guest
+#           and in the host should now match.
 #
-# @delay: continue to deliver ticks at the normal rate.  Guest time will be
-#         delayed due to the late tick
+# @delay: continue to deliver ticks at the normal rate.  The guest OS will
+#         not notice anything is amiss, as from its point of view time will
+#         have continued to flow normally.  The time in the guest should now
+#         be behind the time in the host by exactly the amount of time during
+#         which ticks have been missed.
 #
-# @slew: deliver ticks at a higher rate to catch up with the missed tick. The
-#        guest time should not be delayed once catchup is complete.
+# @slew: deliver ticks at a higher rate to catch up with the missed ticks.
+#        The guest OS will not notice anything is amiss, as from its point
+#        of view time will have continued to flow normally.  Once the timer
+#        has managed to catch up with all the missing ticks, the time in
+#        the guest and in the host should match.
 #
 # Since: 2.0
 ##