From: "Michael S. Tsirkin" <mst@redhat.com>
To: Wei Wang <wei.w.wang@intel.com>
Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org,
qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
kvm@vger.kernel.org, linux-mm@kvack.org, david@redhat.com,
dave.hansen@intel.com, cornelia.huck@de.ibm.com,
akpm@linux-foundation.org, mgorman@techsingularity.net,
aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com,
liliang.opensource@gmail.com, riel@redhat.com, nilal@redhat.com
Subject: Re: [virtio-dev] Re: [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ
Date: Wed, 21 Jun 2017 15:28:56 +0300 [thread overview]
Message-ID: <20170621151922-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <5949E7C0.3050106@intel.com>
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.
I wonder which APIs would Nitesh find useful.
--
MST
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next prev parent reply other threads:[~2017-06-21 12:29 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 [this message]
2017-06-22 8:40 ` Wei Wang
2017-06-28 15:01 ` Michael S. Tsirkin
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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