LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Tiwei Bie <tiwei.bie@intel.com>
To: Jason Wang <jasowang@redhat.com>
Cc: mst@redhat.com, virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	wexu@redhat.com
Subject: Re: [RFC v3 3/5] virtio_ring: add packed ring support
Date: Thu, 10 May 2018 16:56:01 +0800	[thread overview]
Message-ID: <20180510085601.6mpxf3yvwxnqnk5q@debian> (raw)
In-Reply-To: <5885acac-e9e3-3abf-b6a2-7347f4d55be2@redhat.com>

On Thu, May 10, 2018 at 03:34:50PM +0800, Jason Wang wrote:
> On 2018年05月10日 15:32, Jason Wang wrote:
> > On 2018年04月25日 13:15, Tiwei Bie wrote:
> > > +    /* We're using some buffers from the free list. */
> > > +    vq->vq.num_free -= descs_used;
> > > +
> > > +    /* Update free pointer */
> > > +    if (indirect) {
> > > +        n = head + 1;
> > > +        if (n >= vq->vring_packed.num) {
> > > +            n = 0;
> > > +            vq->wrap_counter ^= 1;
> > > +        }
> > > +        vq->next_avail_idx = n;
> > > +    } else
> > > +        vq->next_avail_idx = i;
> > 
> > During testing zerocopy (out of order completion), I found driver may
> > submit two identical buffer id to vhost. So the above code may not work
> > well.
> > 
> > Consider the case that driver adds 3 buffer and virtqueue size is 8.
> > 
> > a) id = 0,count = 2,next_avail = 2
> > 
> > b) id = 2,count = 4,next_avail = 2
> 
> next_avail should be 6 here.
> 
> > 
> > c) id = 4,count = 2,next_avail = 0
> > 
> 
> id should be 6 here.
> 
> Thanks
> 
> > if packet b is done before packet a, driver may think buffer id 0 is
> > available and try to use it if even if the real buffer 0 was not done.
> > 
> > Thanks

Nice catch! Thanks a lot!
I'll implement an ID allocator.

Best regards,
Tiwei Bie

  reply	other threads:[~2018-05-10  8:55 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25  5:15 [RFC v3 0/5] virtio: support packed ring Tiwei Bie
2018-04-25  5:15 ` [RFC v3 1/5] virtio: add packed ring definitions Tiwei Bie
2018-04-25  5:15 ` [RFC v3 2/5] virtio_ring: support creating packed ring Tiwei Bie
2018-04-25  5:15 ` [RFC v3 3/5] virtio_ring: add packed ring support Tiwei Bie
2018-05-10  7:32   ` Jason Wang
2018-05-10  7:34     ` Jason Wang
2018-05-10  8:56       ` Tiwei Bie [this message]
2018-05-10  9:49         ` Jason Wang
2018-05-10 10:50           ` Tiwei Bie
2018-04-25  5:15 ` [RFC v3 4/5] virtio_ring: add event idx support in packed ring Tiwei Bie
2018-05-02  2:51   ` Jason Wang
2018-05-02  7:28     ` Tiwei Bie
2018-05-02 13:51       ` Michael S. Tsirkin
2018-05-02 15:12         ` Tiwei Bie
2018-05-02 15:42           ` Michael S. Tsirkin
2018-05-03  1:11             ` Tiwei Bie
2018-05-03  1:44               ` Michael S. Tsirkin
2018-05-03  2:09                 ` Tiwei Bie
2018-05-03  7:25                   ` Jason Wang
2018-05-03 13:54                     ` Tiwei Bie
2018-05-08  3:05                       ` Jason Wang
2018-05-08  5:40                         ` Jason Wang
2018-05-08  6:44                           ` Tiwei Bie
2018-05-08  7:16                             ` Jason Wang
2018-05-08  9:16                               ` Tiwei Bie
2018-05-08  9:34                                 ` Jason Wang
2018-05-08  9:44                                   ` Tiwei Bie
2018-05-09  3:43                                     ` Jason Wang
2018-05-16  5:01   ` Jason Wang
2018-05-16  5:55     ` Tiwei Bie
2018-04-25  5:15 ` [RFC v3 5/5] virtio_ring: enable " Tiwei Bie
2018-04-27  3:56 ` [RFC v3 0/5] virtio: support " Jason Wang
2018-04-27  4:18   ` Michael S. Tsirkin
2018-04-27  6:17     ` Jason Wang
2018-04-27  9:12       ` Tiwei Bie
2018-04-28  2:45         ` Jason Wang
2018-05-02  3:49 ` Jason Wang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180510085601.6mpxf3yvwxnqnk5q@debian \
    --to=tiwei.bie@intel.com \
    --cc=jasowang@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mst@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=virtualization@lists.linux-foundation.org \
    --cc=wexu@redhat.com \
    --subject='Re: [RFC v3 3/5] virtio_ring: add packed ring support' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).