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From:   David Stevens <stevensd@chromium.org>
Date:   Thu, 5 Mar 2020 17:50:51 +0900
Message-ID: <CAD=HUj7jS5jaRmiJwtGMSQZnR8Qd0VvPkBSbs1d-nATdczWdZA@mail.gmail.com>
Subject: Re: [PATCH v2 4/4] drm/virtio: Support virtgpu exported resources
To:     Gerd Hoffmann <kraxel@redhat.com>
Cc:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Jason Wang <jasowang@redhat.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        open list <linux-kernel@vger.kernel.org>,
        ML dri-devel <dri-devel@lists.freedesktop.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@lists.linux-foundation.org>,
        Linux Media Mailing List <linux-media@vger.kernel.org>,
        linaro-mm-sig@lists.linaro.org, virtio-dev@lists.oasis-open.org
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On Wed, Mar 4, 2020 at 5:01 PM Gerd Hoffmann <kraxel@redhat.com> wrote:
>
>   Hi,
>
> > +     if (vgdev->has_resource_assign_uuid) {
> > +             spin_lock(&vgdev->resource_export_lock);
> > +             if (bo->uuid_state == UUID_NOT_INITIALIZED) {
> > +                     bo->uuid_state = UUID_INITIALIZING;
> > +                     needs_init = true;
> > +             }
> > +             spin_unlock(&vgdev->resource_export_lock);
> > +
> > +             if (needs_init) {
> > +                     ret = virtio_gpu_cmd_resource_assign_uuid(vgdev, bo);
>
> You can submit a fenced command, then wait on the fence here.  Removes
> the need for UUID_INITIALIZING.

Synchronously waiting is simper, but only doing the wait when trying
to use the UUID can help to hide the latency of the virito commands.
That can save quite a bit of time when setting up multiple buffers for
a graphics pipeline, which I think is worthwhile.

-David