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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <564DC13A.2020208@redhat.com>
Date: Thu, 19 Nov 2015 13:31:54 +0100
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Subject: Re: [Qemu-devel] [PATCH] virtio: Implement userspace forwarding for
 host notifiers
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To: Pavel Fedin <p.fedin@samsung.com>, "'Michael S. Tsirkin'" <mst@redhat.com>
Cc: 'Cornelia Huck' <cornelia.huck@de.ibm.com>, 'Christian Borntraeger' <borntraeger@de.ibm.com>, qemu-devel@nongnu.org



On 19/11/2015 13:17, Pavel Fedin wrote:
>  Ok, good. So, this has already been tested. Ok, i think i can further extend this patch by:
> 1. Add a flag to disable memory_region_dispatch_write_ioeventfds(), to be set by KVM code for example. So that with KVM we have even
> smaller performance degradation.
> 2. Issue a one-shot warning, like in my current patch, so that the user knows that his/her kernel prevents from getting the best
> performance.
>  Will it be OK then?

Yes!  However QEMU pretty much always tries to use ioeventfd for virtio.
 I'm not sure you want to warn outside the special cases of vhost or
dataplane...  So perhaps it's better to warn in the vhost and dataplane
case specifically, rather than always.

Paolo