From: Eugenio Perez Martin <eperezma@redhat.com>
To: Jonah Palmer <jonah.palmer@oracle.com>
Cc: qemu-devel@nongnu.org, mst@redhat.com, raphael@enfabrica.net,
kwolf@redhat.com, hreitz@redhat.com, jasowang@redhat.com,
pbonzini@redhat.com, fam@euphon.net, stefanha@redhat.com,
qemu-block@nongnu.org, schalla@marvell.com, leiyang@redhat.com,
virtio-fs@lists.linux.dev, si-wei.liu@oracle.com,
boris.ostrovsky@oracle.com
Subject: Re: [PATCH 4/6] virtio: virtqueue_ordered_flush - VIRTIO_F_IN_ORDER support
Date: Fri, 10 May 2024 09:48:29 +0200 [thread overview]
Message-ID: <CAJaqyWd8ALnpr5BVOFpWo1ndUu9Y3XHO0UKtHFzEOFW3FsmWpA@mail.gmail.com> (raw)
In-Reply-To: <20240506150428.1203387-5-jonah.palmer@oracle.com>
On Mon, May 6, 2024 at 5:06 PM Jonah Palmer <jonah.palmer@oracle.com> wrote:
>
> Add VIRTIO_F_IN_ORDER feature support for virtqueue_flush operations.
>
> The goal of the virtqueue_flush operation when the VIRTIO_F_IN_ORDER
> feature has been negotiated is to write elements to the used/descriptor
> ring in-order and then update used_idx.
>
> The function iterates through the VirtQueueElement used_elems array
> in-order starting at vq->used_idx. If the element is valid (filled), the
> element is written to the used/descriptor ring. This process continues
> until we find an invalid (not filled) element.
>
> If any elements were written, the used_idx is updated.
>
> Tested-by: Lei Yang <leiyang@redhat.com>
> Signed-off-by: Jonah Palmer <jonah.palmer@oracle.com>
> ---
> hw/virtio/virtio.c | 75 +++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 74 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 064046b5e2..0efed2c88e 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -1006,6 +1006,77 @@ static void virtqueue_packed_flush(VirtQueue *vq, unsigned int count)
> }
> }
>
> +static void virtqueue_ordered_flush(VirtQueue *vq)
> +{
> + unsigned int i = vq->used_idx;
> + unsigned int ndescs = 0;
> + uint16_t old = vq->used_idx;
> + bool packed;
> + VRingUsedElem uelem;
> +
> + packed = virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED);
> +
> + if (packed) {
> + if (unlikely(!vq->vring.desc)) {
> + return;
> + }
> + } else if (unlikely(!vq->vring.used)) {
> + return;
> + }
> +
> + /* First expected in-order element isn't ready, nothing to do */
> + if (!vq->used_elems[i].filled) {
> + return;
> + }
> +
> + /* Write first expected in-order element to used ring (split VQs) */
> + if (!packed) {
> + uelem.id = vq->used_elems[i].index;
> + uelem.len = vq->used_elems[i].len;
> + vring_used_write(vq, &uelem, i);
> + }
> +
> + ndescs += vq->used_elems[i].ndescs;
> + i += ndescs;
> + if (i >= vq->vring.num) {
> + i -= vq->vring.num;
> + }
> +
> + /* Search for more filled elements in-order */
> + while (vq->used_elems[i].filled) {
> + if (packed) {
> + virtqueue_packed_fill_desc(vq, &vq->used_elems[i], ndescs, false);
> + } else {
> + uelem.id = vq->used_elems[i].index;
> + uelem.len = vq->used_elems[i].len;
> + vring_used_write(vq, &uelem, i);
> + }
> +
> + vq->used_elems[i].filled = false;
> + ndescs += vq->used_elems[i].ndescs;
> + i += ndescs;
> + if (i >= vq->vring.num) {
> + i -= vq->vring.num;
> + }
> + }
> +
I may be missing something, but you have split out the first case as a
special one, totally out of the while loop. Can't it be contained in
the loop checking !(packed && i == vq->used_idx)? That would avoid
code duplication.
A comment can be added in the line of "first entry of packed is
written the last so the guest does not see invalid descriptors".
> + if (packed) {
> + virtqueue_packed_fill_desc(vq, &vq->used_elems[vq->used_idx], 0, true);
> + vq->used_idx += ndescs;
> + if (vq->used_idx >= vq->vring.num) {
> + vq->used_idx -= vq->vring.num;
> + vq->used_wrap_counter ^= 1;
> + vq->signalled_used_valid = false;
> + }
> + } else {
> + vring_used_idx_set(vq, i);
> + if (unlikely((int16_t)(i - vq->signalled_used) < (uint16_t)(i - old))) {
> + vq->signalled_used_valid = false;
> + }
> + }
> + vq->inuse -= ndescs;
> +}
> +
> void virtqueue_flush(VirtQueue *vq, unsigned int count)
> {
> if (virtio_device_disabled(vq->vdev)) {
> @@ -1013,7 +1084,9 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
> return;
> }
>
> - if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_IN_ORDER)) {
> + virtqueue_ordered_flush(vq);
> + } else if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> virtqueue_packed_flush(vq, count);
> } else {
> virtqueue_split_flush(vq, count);
> --
> 2.39.3
>
next prev parent reply other threads:[~2024-05-10 7:49 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 15:04 [PATCH 0/6] virtio,vhost: Add VIRTIO_F_IN_ORDER support Jonah Palmer
2024-05-06 15:04 ` [PATCH 1/6] virtio: Add bool to VirtQueueElement Jonah Palmer
2024-05-09 12:32 ` Eugenio Perez Martin
2024-05-10 10:26 ` Jonah Palmer
2024-05-06 15:04 ` [PATCH 2/6] virtio: virtqueue_pop - VIRTIO_F_IN_ORDER support Jonah Palmer
2024-05-09 13:13 ` Eugenio Perez Martin
2024-05-10 10:52 ` Jonah Palmer
2024-05-06 15:04 ` [PATCH 3/6] virtio: virtqueue_ordered_fill " Jonah Palmer
2024-05-09 14:08 ` Eugenio Perez Martin
2024-05-10 12:01 ` Jonah Palmer
2024-05-06 15:04 ` [PATCH 4/6] virtio: virtqueue_ordered_flush " Jonah Palmer
2024-05-10 7:48 ` Eugenio Perez Martin [this message]
2024-05-10 13:07 ` Jonah Palmer
2024-05-06 15:04 ` [PATCH 5/6] vhost,vhost-user: Add VIRTIO_F_IN_ORDER to vhost feature bits Jonah Palmer
2024-05-06 15:04 ` [PATCH 6/6] virtio: Add VIRTIO_F_IN_ORDER property definition Jonah Palmer
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