Re: [Xen-devel] [PATCH 0/2] enable event channel wake-up for mem_event interfaces

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 28/09/2011 14:22, "Adin Scannell" <adin@xxxxxxxxxxxxxxx> wrote:

> Currently the mem_event code requires a domctl to kick the hypervisor
> and unpause vcpus.  An event channel is used to notify dom0 of
> requests placed in the ring, and it can similarly be used to notify
> Xen, so as not to overuse domctls when running many domains with
> mem_event interfaces (domctls are not a great interface for this sort
> of thing, because they will all be serialized).
> 
> This patch set enables the use of the event channel to signal when a
> response in placed in a mem_event ring.

I don't have an opinion on patch 1/2. I'll leave it to someone else, like
Tim, to comment.

Patch 2/2 I don't mind the principle, but the implementation is not very
scalable. I will post a rewritten version to the list. It might be early
next week before I do so.

 -- Keir

> The two patches are as follows:
> - The first patch tweaks the memevent code to ensure that no events
> are lost.  Instead of calling get_response once per kick, we may have
> to pull out multiple events at a time.  This doesn't affect normal
> operation with the domctls.
> This patch also ensures that each vCPU can generate a request in each
> mem_event ring (i.e. put_request will always work), by appropriately
> pausing vCPUs when after requests are placed.
> - The second patch breaks the Xen-side event channel handling into a
> new arch-specific file "events.c", and adds cases for the different
> Xen-handled event channels.  This formalizes the tiny exception that
> was in place for just qemu in event_channel.c.
> 
> All the domctls are still in place and everything should be backwards
> compatible.
> 
> Cheers,
> -Adin
> 
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