Re: [Xen-devel] Wait queue support for 4.3

[Andres Lagar-Cavilla <andreslc@xxxxxxxxxxxxxx>]

On Oct 12, 2012, at 12:30 PM, Keir Fraser wrote:

> On 12/10/2012 16:38, "Andres Lagar-Cavilla" <andreslc@xxxxxxxxxxxxxx> wrote:
> 
>> During the last Xen Summit there were informal discussions about the status 
>> of
>> wait queues in the hypervisor.
>> 
>> To recap:
>> 1. Wait queues are used in mem event, when events generated by a vcpu 
>> overflow
>> the ring size
>> 2. We would like to use wait queues when the hypervisor needs a paged out
>> frame (say for hvm_copy)
>> 3. We would like to use wait queues to avoid the two decoupled mmio emulation
>> passes
>> 4. We would like to use wait queues when the hypervisor needs write access to
>> a shared frame (say for hvm copy), and unsharing temporarily fails with
>> ENOMEM.
>> 
>> Conceivably more uses for wait queues may come down the line.
>> 
>> Use-cases 2. and 4. were left out of the time frame of 4.2, because a vcpu
>> cannot go to sleep on a wait queue while holding a spinlock, and such
>> situations would frequently arise. Preliminary patches from Tim Deegan have
>> floated on the list
>> (http://lists.xen.org/archives/html/xen-devel/2012-02/msg02133.html). We 
>> would
>> like this functionality to be present on the mm side for 4.3, and then 
>> proceed
>> to remove the "thinking" that consumers of the p2m interface now need to
>> perform.
>> 
>> The current maintainer (effectively) for wait queues is Keir. Keir, any ideas
>> on a schedule for the cleanup?
> 
> I maintain the wait-queue mechanism, but not every (potential) user of it!

That's the end of my cunning scheme. It was worth a try ...

> The only use-case above that might fall into my domain is 3, I think.

So perhaps mm should wait for that to happen to then tackle wait queues for 
paging/sharing?

Thanks,
Andres

> 
> -- Keir
> 
>> Thanks
>> Andres
>> 
> 
> 


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