Re: [Xen-devel] Question about the ability of credit scheduler to handle I/O and CPU intensive VMs

[Yuehai Xu <yuehaixu@xxxxxxxxx>]

> The file you're looking for re getting an event channel is
> xen/common/schedule.c, the common scheduling code.
>
> In schedule.c, vcpu_wake() will always call the scheduler wake()
> function;  However, event channels and other "you have an event"
> functions call call vcpu_unblock() instead, which will check the
> vcpu's VPF_blocked flag and only call vcpu_wake if it was set.
>
> You could try changing vcpu_unblock() to always call vcpu_wake() for
> your experimental development; I'm not sure what side-effects this
> would have.

After changing vcpu_unblock() to always call vcpu_wake(), the VM that
has event can be scheduled immediately no matter whether it is CPU
intensive. However, I have another question. Except the I/O event, it
seems there are many other events too. Our design is to give a VM a
very short period of time when it has "I/O event", and right now,
vcpu_wake() is invoked when an event comes, even it is not "I/O
event", this will cause that the VM is scheduled much more frequently
than what I except.

For example, suppose 2 VMs, one is CPU intensive and another is CPU +
I/O intensive, from the level of scheduler, almost the same number of
events are received from the two VMs. Even I/O itself creates event,
since there are other events, the total number of events are almost
the same. In such case, I think we need to differentiate the I/O
events from other events.

I add trace point to __run_tickle() and notice the result that the
number of events are almost the same from two VMs, one of which is CPU
intensive and the other is CPU + I/O intensive. Although I do not
completely confirm what I have said currently, I need do more
experiments.

Is it possible for me to detect the "I/O event" from "event" so that I
can give VM that has "I/O event" the priority to be scheduled
immediately?

Thanks,
Yuehai

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