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Re: [PATCH v3 07/20] virtio: add vhost-user-base and a generic vhost-use
From: |
Alex Bennée |
Subject: |
Re: [PATCH v3 07/20] virtio: add vhost-user-base and a generic vhost-user-device |
Date: |
Tue, 05 Sep 2023 18:01:56 +0100 |
User-agent: |
mu4e 1.11.16; emacs 29.1.50 |
Matias Ezequiel Vara Larsen <mvaralar@redhat.com> writes:
> On Mon, Jul 10, 2023 at 04:35:09PM +0100, Alex Bennée wrote:
>> In theory we shouldn't need to repeat so much boilerplate to support
>> vhost-user backends. This provides a generic vhost-user-base QOM
>> object and a derived vhost-user-device for which the user needs to
>> provide the few bits of information that aren't currently provided by
>> the vhost-user protocol. This should provide a baseline implementation
>> from which the other vhost-user stub can specialise.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>
>> ---
>> v2
>> - split into vub and vud
<snip>
>> +
>> + /*
>> + * Disable guest notifiers, by default all notifications will be via the
>> + * asynchronous vhost-user socket.
>> + */
>> + vdev->use_guest_notifier_mask = false;
>> +
>> + /* Allocate queues */
>> + vub->vqs = g_ptr_array_sized_new(vub->num_vqs);
>> + for (int i = 0; i < vub->num_vqs; i++) {
>> + g_ptr_array_add(vub->vqs,
>> + virtio_add_queue(vdev, 4, vub_handle_output));
>> + }
>> +
>
> Hello Alex, apologies if someone already asked this. If I understand
> correctly, the second parameter of virtio_add_queue() is the len of the
> queue. Why have you chosen "4" as its value? Shall qemu query the len of
> the queue from the vhost-user device instead?
Hmm yeah that is inherited from the virtio-rng backend which has a
pretty short queue. I don't think it is intrinsic to the device
implementation (although I guess that depends if a device will have
multiple requests in flight).
I propose making is some useful ^2 (like 64) and adding a config knob to
increase it if needed.
--
Alex Bennée
Virtualisation Tech Lead @ Linaro