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, "K. Den" <den@klaipeden.com>,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH net] Revert "vhost: cache used event for better performance"
Date: Wed, 9 Aug 2017 07:37:11 +0300 [thread overview]
Message-ID: <20170809073422-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <6698b85c-18f4-17e6-db70-7708692fb761@redhat.com>
On Wed, Aug 09, 2017 at 10:38:10AM +0800, Jason Wang wrote:
> I think don't think current code can work well if vq.num is grater than
> 2^15. Since all cached idx is u16. This looks like a bug which needs to be
> fixed.
That's a limitation of virtio 1.0.
> > * else if the interval of vq.num is [2^15, 2^16):
> > the logic in the original patch (809ecb9bca6a9) suffices
> > * else (= less than 2^15) (optional):
> > checking only (vring_need_event(vq->last_used_event, new + vq->num, new)
> > would suffice.
> >
> > Am I missing something, or is this irrelevant?
Could you pls repost the suggestion copying virtio-dev mailing list
(subscriber only, sorry about that, but host/guest ABI discussions
need to copy that list)?
> Looks not, I think this may work. Let me do some test.
>
> Thanks
I think that at this point it's prudent to add a feature bit
as the virtio spec does not require to never move the event index back.
WARNING: multiple messages have this Message-ID (diff)
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Jason Wang <jasowang@redhat.com>
Cc: "K. Den" <den@klaipeden.com>,
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, 9 Aug 2017 07:37:11 +0300 [thread overview]
Message-ID: <20170809073422-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <6698b85c-18f4-17e6-db70-7708692fb761@redhat.com>
On Wed, Aug 09, 2017 at 10:38:10AM +0800, Jason Wang wrote:
> I think don't think current code can work well if vq.num is grater than
> 2^15. Since all cached idx is u16. This looks like a bug which needs to be
> fixed.
That's a limitation of virtio 1.0.
> > * else if the interval of vq.num is [2^15, 2^16):
> > the logic in the original patch (809ecb9bca6a9) suffices
> > * else (= less than 2^15) (optional):
> > checking only (vring_need_event(vq->last_used_event, new + vq->num, new)
> > would suffice.
> >
> > Am I missing something, or is this irrelevant?
Could you pls repost the suggestion copying virtio-dev mailing list
(subscriber only, sorry about that, but host/guest ABI discussions
need to copy that list)?
> Looks not, I think this may work. Let me do some test.
>
> Thanks
I think that at this point it's prudent to add a feature bit
as the virtio spec does not require to never move the event index back.
next prev parent reply other threads:[~2017-08-09 4:37 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 11:56 ` Jason Wang
2017-07-26 11:56 ` Jason Wang
2017-07-26 10:53 ` Christian Borntraeger
2017-07-26 12:57 ` Michael S. Tsirkin
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 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 [this message]
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 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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