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From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 2/3] vhost_net: support in order feature
Date: Mon, 26 Nov 2018 11:52:07 +0800	[thread overview]
Message-ID: <1c50dc69-49d5-0d19-dea9-4c97a2d99b5f@redhat.com> (raw)
In-Reply-To: <20181123104333-mutt-send-email-mst@kernel.org>


On 2018/11/23 下午11:49, Michael S. Tsirkin wrote:
> On Fri, Nov 23, 2018 at 11:00:15AM +0800, Jason Wang wrote:
>> This makes vhost_net to support in order feature. This is as simple as
>> use datacopy path when it was negotiated. An alternative is not to
>> advertise in order when zerocopy is enabled which tends to be
>> suboptimal consider zerocopy may suffer from e.g HOL issues.
> Well IIRC vhost_zerocopy_signal_used is used to
> actually reorder used ring to match available ring.
> So with a big comment explaining why it is so,
> we could just enable IN_ORDER there too.
>

The problem is we allow switching between zerocopy and datacopy.

And what's more important, if we allow in order for zerocopy, a single 
packet delay may hang all the rest.

Thanks


WARNING: multiple messages have this Message-ID (diff)
From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@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-next 2/3] vhost_net: support in order feature
Date: Mon, 26 Nov 2018 11:52:07 +0800	[thread overview]
Message-ID: <1c50dc69-49d5-0d19-dea9-4c97a2d99b5f@redhat.com> (raw)
In-Reply-To: <20181123104333-mutt-send-email-mst@kernel.org>


On 2018/11/23 下午11:49, Michael S. Tsirkin wrote:
> On Fri, Nov 23, 2018 at 11:00:15AM +0800, Jason Wang wrote:
>> This makes vhost_net to support in order feature. This is as simple as
>> use datacopy path when it was negotiated. An alternative is not to
>> advertise in order when zerocopy is enabled which tends to be
>> suboptimal consider zerocopy may suffer from e.g HOL issues.
> Well IIRC vhost_zerocopy_signal_used is used to
> actually reorder used ring to match available ring.
> So with a big comment explaining why it is so,
> we could just enable IN_ORDER there too.
>

The problem is we allow switching between zerocopy and datacopy.

And what's more important, if we allow in order for zerocopy, a single 
packet delay may hang all the rest.

Thanks

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  reply	other threads:[~2018-11-26  3:52 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-23  3:00 [PATCH net-next 0/3] basic in order support for vhost_net Jason Wang
2018-11-23  3:00 ` [PATCH net-next 1/3] virtio: introduce in order feature bit Jason Wang
2018-11-23  3:00 ` Jason Wang
2018-11-23  3:00 ` [PATCH net-next 2/3] vhost_net: support in order feature Jason Wang
2018-11-23  3:00 ` Jason Wang
2018-11-23 15:49   ` Michael S. Tsirkin
2018-11-26  3:52     ` Jason Wang [this message]
2018-11-26  3:52       ` Jason Wang
2018-11-23 15:49   ` Michael S. Tsirkin
2018-11-23  3:00 ` [PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated Jason Wang
2018-11-23  3:00 ` Jason Wang
2018-11-23 15:41   ` Michael S. Tsirkin
2018-11-23 15:41   ` Michael S. Tsirkin
2018-11-26  4:01     ` Jason Wang
2018-11-26  4:01       ` Jason Wang

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