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: "Michael S. Tsirkin" <mst@redhat.com>,
	virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	wexu@redhat.com, jfreimann@redhat.com
Subject: Re: [RFC v3 0/5] virtio: support packed ring
Date: Fri, 27 Apr 2018 17:12:34 +0800	[thread overview]
Message-ID: <20180427091234.n6vr3wcnbnqxd3so@debian> (raw)
In-Reply-To: <5c712aa2-f00e-b472-cdfc-48175aea790d@redhat.com>

On Fri, Apr 27, 2018 at 02:17:51PM +0800, Jason Wang wrote:
> On 2018年04月27日 12:18, Michael S. Tsirkin wrote:
> > On Fri, Apr 27, 2018 at 11:56:05AM +0800, Jason Wang wrote:
> > > On 2018年04月25日 13:15, Tiwei Bie wrote:
> > > > Hello everyone,
> > > > 
> > > > This RFC implements packed ring support in virtio driver.
> > > > 
> > > > Some simple functional tests have been done with Jason's
> > > > packed ring implementation in vhost:
> > > > 
> > > > https://lkml.org/lkml/2018/4/23/12
> > > > 
> > > > Both of ping and netperf worked as expected (with EVENT_IDX
> > > > disabled). But there are below known issues:
> > > > 
> > > > 1. Reloading the guest driver will break the Tx/Rx;
> > > Will have a look at this issue.
> > > 
> > > > 2. Zeroing the flags when detaching a used desc will
> > > >      break the guest -> host path.
> > > I still think zeroing flags is unnecessary or even a bug. At host, I track
> > > last observed avail wrap counter and detect avail like (what is suggested in
> > > the example code in the spec):
> > > 
> > > static bool desc_is_avail(struct vhost_virtqueue *vq, __virtio16 flags)
> > > {
> > >         bool avail = flags & cpu_to_vhost16(vq, DESC_AVAIL);
> > > 
> > >         return avail == vq->avail_wrap_counter;
> > > }
> > > 
> > > So zeroing wrap can not work with this obviously.
> > > 
> > > Thanks
> > I agree. I think what one should do is flip the available bit.
> > 
> 
> But is this flipping a must?
> 
> Thanks

Yeah, that's my question too. It seems to be a requirement
for driver that, the only change to the desc status that a
driver can do during running is to mark the desc as avail,
and any other changes to the desc status are not allowed.
Similarly, the device can only mark the desc as used, and
any other changes to the desc status are also not allowed.
So the question is, are there such requirements?

Based on below contents in the spec:

"""
Thus VIRTQ_DESC_F_AVAIL and VIRTQ_DESC_F_USED bits are different
for an available descriptor and equal for a used descriptor.

Note that this observation is mostly useful for sanity-checking
as these are necessary but not sufficient conditions
"""

It seems that, it's necessary for devices to check whether
the AVAIL bit and USED bit are different.

Best regards,
Tiwei Bie

  reply	other threads:[~2018-04-27  9:11 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25  5:15 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
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 [this message]
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=20180427091234.n6vr3wcnbnqxd3so@debian \
    --to=tiwei.bie@intel.com \
    --cc=jasowang@redhat.com \
    --cc=jfreimann@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 0/5] virtio: support packed ring' \
    /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).