[Xen-devel] [PATCH] strictly increasing hvm guest time

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

This simple one-line patch changes hvm guest time from
monotonically non-decreasing to monotonically strictly-
increasing.  As a result, two consecutive reads of the
(virtual) hpet will never return the same value, thus
avoiding the appearance that time has stopped (which may
occur if there is skew between physical processor TSCs).

The only problem scenario I can see is if:

1) N = number of physical CPUs on system
2) T = time in nsec of fastest call P that an hvm guest can
   make that indirectly invokes hvm_get_guest_time()
3) N>T (highly unlikely)
4) guests on all N physical CPUs are continuously
   calling P (also highly unlikely)

then guest time could accelerate faster than Xen system
time.

Dan

===================================
Thanks... for the memory
I really could use more / My throughput's on the floor
The balloon is flat / My swap disk's fat / I've OOM's in store
Overcommitted so much
(with apologies to the late great Bob Hope)

Attachment: hvmmono.patch
Description: Binary data

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