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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] Revert "vhost: cache used event for better performance"
Date: Wed, 26 Jul 2017 21:18:02 +0800	[thread overview]
Message-ID: <117542fc-eef9-c043-7c9e-daafceb7db4e@redhat.com> (raw)
In-Reply-To: <20170726155435-mutt-send-email-mst@kernel.org>



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

  reply	other threads:[~2017-07-26 13:18 UTC|newest]

Thread overview: 26+ 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 10:53 ` Christian Borntraeger
2017-07-26 11:56   ` Jason Wang
2017-07-26 11:56     ` Jason Wang
2017-07-26 12:57 ` Michael S. Tsirkin
2017-07-26 12:57   ` Michael S. Tsirkin
2017-07-26 13:18   ` Jason Wang [this message]
2017-07-26 13:37     ` Jason Wang
2017-07-26 16:08       ` Michael S. Tsirkin
2017-07-26 16:08         ` Michael S. Tsirkin
2017-07-30  6:26         ` K. Den
2017-07-30  6:26         ` K. Den
2017-08-09  2:38           ` Jason Wang
2017-08-09  2:38             ` Jason Wang
2017-08-09  4:37             ` Michael S. Tsirkin
2017-08-09  4:37               ` Michael S. Tsirkin
2017-08-13 14:11               ` Koichiro Den
2017-08-13 14:11                 ` Koichiro Den
2017-08-13 16:12                 ` Koichiro Den
2017-08-13 16:12                   ` Koichiro Den
2017-07-26 13:37     ` Jason Wang
2017-07-26 15:21     ` Michael S. Tsirkin
2017-07-26 15:21     ` Michael S. Tsirkin
2017-07-26 13:18   ` Jason Wang
  -- strict thread matches above, loose matches on Subject: below --
2017-07-26  8:03 Jason Wang

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