From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org, virtualization@lists.linux-foundation.org
Subject: Re: [PATCH net] Revert "vhost: cache used event for better performance"
Date: Wed, 26 Jul 2017 19:08:26 +0300 [thread overview]
Message-ID: <20170726190745-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <6b3a9a98-c095-1729-3528-dd521f136797@redhat.com>
On Wed, Jul 26, 2017 at 09:37:15PM +0800, Jason Wang wrote:
>
>
> On 2017年07月26日 21:18, Jason Wang wrote:
> >
> >
> > On 2017年07月26日 20:57, Michael S. Tsirkin wrote:
> > > On Wed, Jul 26, 2017 at 04:03:17PM +0800, Jason Wang wrote:
> > > > This reverts commit 809ecb9bca6a9424ccd392d67e368160f8b76c92. Since it
> > > > was reported to break vhost_net. We want to cache used event and use
> > > > it to check for notification. We try to valid cached used event by
> > > > checking whether or not it was ahead of new, but this is not correct
> > > > all the time, it could be stale and there's no way to know about this.
> > > >
> > > > Signed-off-by: Jason Wang<jasowang@redhat.com>
> > > Could you supply a bit more data here please? How does it get stale?
> > > What does guest need to do to make it stale? This will be helpful if
> > > anyone wants to bring it back, or if we want to extend the protocol.
> > >
> >
> > The problem we don't know whether or not guest has published a new used
> > event. The check vring_need_event(vq->last_used_event, new + vq->num,
> > new) is not sufficient to check for this.
> >
> > Thanks
>
> More notes, the previous assumption is that we don't move used event back,
> but this could happen in fact if idx is wrapper around.
You mean if the 16 bit index wraps around after 64K entries.
Makes sense.
> Will repost and add
> this into commit log.
>
> Thanks
_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization
next prev parent reply other threads:[~2017-07-26 16:08 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-26 8:03 [PATCH net] Revert "vhost: cache used event for better performance" Jason Wang
2017-07-26 10:53 ` Christian Borntraeger
2017-07-26 11:56 ` Jason Wang
2017-07-26 12:57 ` Michael S. Tsirkin
2017-07-26 13:18 ` Jason Wang
2017-07-26 13:37 ` Jason Wang
2017-07-26 16:08 ` Michael S. Tsirkin [this message]
2017-07-30 6:26 ` K. Den
2017-08-09 2:38 ` Jason Wang
2017-08-09 4:37 ` Michael S. Tsirkin
2017-08-13 14:11 ` Koichiro Den
2017-08-13 16:12 ` Koichiro Den
2017-07-26 15:21 ` Michael S. Tsirkin
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=20170726190745-mutt-send-email-mst@kernel.org \
--to=mst@redhat.com \
--cc=jasowang@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=virtualization@lists.linux-foundation.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).