[PATCH v2 0/2] Automatically grab wallclock time updates from hypervisor

From: Glauber Costa
Date: Wed Sep 02 2009 - 10:08:48 EST

i folks,

In this proposed patch, I am introducing a worker fired by kvmclock that updates
guest wallclock periodically to reflect changes in the host's wallclock. With this
patch, a large pool of VMs will no longer have to run NTP in all of its guests.

The worker does that at a configurable interval, with a minimum granularity of 1
second. So, although not exactly cheap, the msr write needed to get an updated
wallclock value won't pose a heavy burden on the system.

It is also possible to disable it completely if this behaviour is undesired for
a specific scenario.

Changes from v1:
* disabled by default
* adjust clock in a loop, to prevent agaist host scheduling.

diffstat follows:

arch/x86/include/asm/kvm_para.h | 6 +++
arch/x86/kernel/kvmclock.c | 85 ++++++++++++++++++++++++++++++++++----
kernel/sysctl.c | 13 ++++++
3 files changed, 95 insertions(+), 9 deletions(-)

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