On 02/07/2011 07:14 AM, Avi Kivity wrote:
On 02/07/2011 03:11 PM, Anthony Liguori wrote:
On 02/07/2011 06:34 AM, Avi Kivity wrote:
On 02/04/2011 10:56 AM, Jan Kiszka wrote:
>
> This should be a rare event. If you are missing 50% of your
> notifications, not amount of gradual catchup is going to help
you out.
But that's the only thing this patch is after: lost ticks at QEMU
level.
Most lost ticks will happen at the vcpu level. The iothread has low
utilization and will therefore be scheduled promptly, whereas the
vcpu thread may have high utilization and will thus be preempted.
When it is preempted for longer than the timer tick, we will see
vcpu-level coalescing. All it takes is 2:1 overcommit to see time
go half as fast; I don't think you'll ever see that on bare metal.
But that's not to say that doing something about lost ticks in QEMU
isn't still useful.
If it doesn't solve the majority of the problems it isn't very useful
IMO. It's a good first step, but not sufficient for real world use
with overcommit.
Even if we have a way to detect coalescing, we still need to make sure
we don't lose ticks in QEMU. So regardless of whether it solves the
majority of problems, we need this anyway.
Regards,
Anthony Liguori
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