From: "Michael S. Tsirkin" <mst@redhat.com>
To: Wei Wang <wei.w.wang@intel.com>
Cc: "virtio-dev@lists.oasis-open.org"
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"nilal@redhat.com" <nilal@redhat.com>
Subject: Re: [virtio-dev] Re: [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ
Date: Wed, 28 Jun 2017 18:01:58 +0300 [thread overview]
Message-ID: <20170628175956-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <594B8287.6000706@intel.com>
On Thu, Jun 22, 2017 at 04:40:39PM +0800, Wei Wang wrote:
> On 06/21/2017 08:28 PM, Michael S. Tsirkin wrote:
> > On Wed, Jun 21, 2017 at 11:28:00AM +0800, Wei Wang wrote:
> > > On 06/21/2017 12:18 AM, Michael S. Tsirkin wrote:
> > > > On Fri, Jun 09, 2017 at 06:41:41PM +0800, Wei Wang wrote:
> > > > > - if (!virtqueue_indirect_desc_table_add(vq, desc, num)) {
> > > > > + if (!virtqueue_indirect_desc_table_add(vq, desc, *num)) {
> > > > > virtqueue_kick(vq);
> > > > > - wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> > > > > - vb->balloon_page_chunk.chunk_num = 0;
> > > > > + if (busy_wait)
> > > > > + while (!virtqueue_get_buf(vq, &len) &&
> > > > > + !virtqueue_is_broken(vq))
> > > > > + cpu_relax();
> > > > > + else
> > > > > + wait_event(vb->acked, virtqueue_get_buf(vq, &len));
> > > > This is something I didn't previously notice.
> > > > As you always keep a single buffer in flight, you do not
> > > > really need indirect at all. Just add all descriptors
> > > > in the ring directly, then kick.
> > > >
> > > > E.g.
> > > > virtqueue_add_first
> > > > virtqueue_add_next
> > > > virtqueue_add_last
> > > >
> > > > ?
> > > >
> > > > You also want a flag to avoid allocations but there's no need to do it
> > > > per descriptor, set it on vq.
> > > >
> > > Without using the indirect table, I'm thinking about changing to use
> > > the standard sg (i.e. struct scatterlist), instead of vring_desc, so that
> > > we don't need to modify or add any new functions of virtqueue_add().
> > >
> > > In this case, we will kmalloc an array of sgs in probe(), and we can add
> > > the sgs one by one to the vq, which won't trigger the allocation of an
> > > indirect table inside virtqueue_add(), and then kick when all are added.
> > >
> > > Best,
> > > Wei
> > And allocate headers too? This can work. API extensions aren't
> > necessarily a bad idea though. The API I suggest above is preferable
> > for the simple reason that it can work without INDIRECT flag
> > support in hypervisor.
>
> OK, probably we don't need to add a desc to the vq - we can just use
> the vq's desc, like this:
>
> int virtqueue_add_first(struct virtqueue *_vq,
> uint64_t addr,
> uint32_t len,
> bool in,
> unsigned int *idx) {
>
> ...
> uint16_t desc_flags = in ? VRING_DESC_F_NEXT | VRING_DESC_F_WRITE :
> VRING_DESC_F_NEXT;
>
> vq->vring.desc[vq->free_head].addr = addr;
> vq->vring.desc[vq->free_head].len = len;
> vq->vring.desc[vq->free_head].flags = cpu_to_virtio16(_vq->vdev, flags);
> /* return to the caller the desc id */
> *idx = vq->free_head;
> ...
> }
>
> int virtqueue_add_next(struct virtqueue *_vq,
> uint64_t addr,
> uint32_t len,
> bool in,
> bool end,
> unsigned int *idx) {
> ...
> vq->vring.desc[*idx].next = vq->free_head;
> vq->vring.desc[vq->free_head].addr = addr;
> ...
> if (end)
> remove the VRING_DESC_F_NEXT flag
> }
>
Add I would say add-last.
>
> What do you think? We can also combine the two functions into one.
>
>
>
> Best,
> Wei
With an enum? Yes that's also an option.
--
MST
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next prev parent reply other threads:[~2017-06-28 15:02 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-09 10:41 [PATCH v11 0/6] Virtio-balloon Enhancement Wei Wang
2017-06-09 10:41 ` [PATCH v11 1/6] virtio-balloon: deflate via a page list Wei Wang
2017-06-09 10:41 ` [PATCH v11 2/6] virtio-balloon: coding format cleanup Wei Wang
2017-06-09 10:41 ` [PATCH v11 3/6] virtio-balloon: VIRTIO_BALLOON_F_PAGE_CHUNKS Wei Wang
2017-06-13 17:56 ` Michael S. Tsirkin
2017-06-13 17:59 ` Dave Hansen
2017-06-13 18:55 ` Michael S. Tsirkin
2017-06-15 8:10 ` [virtio-dev] " Wei Wang
2017-06-16 3:19 ` Michael S. Tsirkin
2017-06-28 15:04 ` Matthew Wilcox
2017-07-12 13:05 ` Wei Wang
2017-06-09 10:41 ` [PATCH v11 4/6] mm: function to offer a page block on the free list Wei Wang
2017-06-12 14:10 ` Dave Hansen
2017-06-12 16:28 ` Michael S. Tsirkin
2017-06-12 16:42 ` Dave Hansen
2017-06-12 20:34 ` Michael S. Tsirkin
2017-06-12 20:54 ` Dave Hansen
2017-06-13 2:56 ` Wei Wang
2017-06-20 16:44 ` Rik van Riel
2017-06-20 16:49 ` David Hildenbrand
2017-06-20 17:29 ` Rik van Riel
2017-06-20 18:26 ` Michael S. Tsirkin
2017-06-20 19:51 ` Rik van Riel
2017-06-21 12:41 ` Michael S. Tsirkin
2017-06-21 8:38 ` [Qemu-devel] " Wei Wang
2017-06-20 18:17 ` Michael S. Tsirkin
2017-06-20 18:54 ` David Hildenbrand
2017-06-20 18:56 ` Michael S. Tsirkin
2017-06-20 19:01 ` David Hildenbrand
2017-06-21 12:56 ` Christian Borntraeger
2017-06-21 13:47 ` David Hildenbrand
2017-06-09 10:41 ` [PATCH v11 5/6] mm: export symbol of next_zone and first_online_pgdat Wei Wang
2017-06-09 10:41 ` [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Wei Wang
2017-06-12 14:07 ` Dave Hansen
2017-06-13 10:17 ` Wei Wang
2017-06-20 16:18 ` Michael S. Tsirkin
2017-06-21 3:28 ` [virtio-dev] " Wei Wang
2017-06-21 12:28 ` Michael S. Tsirkin
2017-06-22 8:40 ` Wei Wang
2017-06-28 15:01 ` Michael S. Tsirkin [this message]
2017-07-12 12:57 ` Wei Wang
2017-06-09 11:18 ` [PATCH v11 0/6] Virtio-balloon Enhancement Wang, Wei W
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