Re: [Xen-devel] RFC: mem_event: use wait queue when ring is full

[Olaf Hering <olaf@xxxxxxxxx>]

On Tue, Nov 22, Andres Lagar-Cavilla wrote:

> Olaf, two questions here
> 
> - do you have any insight for events caused by foreign mappings? Those
> will be lost with a full ring, with or without wait queues

The callers of mem_event_check_ring() have to retry if the ring is full.
Thats what happens with p2m_mem_paging_populate(), the callers return
-ENOENT and expect a retry at some later point.

> - we have posted a patch (twice) previously, with changes to ring
> management, most importantly sending guest vcpus to sleep when space in
> the ring is < d->max_vcpus. I see these two patches as complementary. What
> is your take?

I'm not proposing to include my patch as is, because it has one issue:
wake_up will start all waiting vcpus even if there is just a single slot
free in the ringbuffer. You patch is better in this respect because only
a few will be started again.

I will send comments for it later.

Olaf

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