From: Stephen Hemminger <stephen@networkplumber.org>
To: Yong Wang <yongwang@vmware.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v3 1/4] vmxnet3: restore tx data ring support
Date: Tue, 12 Jan 2016 20:50:22 -0800 [thread overview]
Message-ID: <20160112205022.118c3423@xeon-e3> (raw)
In-Reply-To: <6EDC655B-0C21-4C63-997D-87BD2B35BAEB@vmware.com>
On Wed, 13 Jan 2016 02:20:01 +0000
Yong Wang <yongwang@vmware.com> wrote:
> >Good idea to use a local region which optmizes the copy in the host,
> >but this implementation needs to be more general.
> >
> >As written it is broken for multi-segment packets. A multi-segment
> >packet will have a pktlen >= datalen as in:
> > m -> mb_segs=3, pktlen=1200, datalen=200
> > -> datalen=900
> > -> datalen=100
> >
> >There are two ways to fix this. You could test for nb_segs == 1
> >or better yet. Optimize each segment it might be that the first
> >segment (or tail segment) would fit in the available data area.
>
> Currently the vmxnet3 backend has a limitation of 128B data area so
> it should work even for the multi-segmented pkt shown above. But
> I agree it does not work for all multi-segmented packets. The
> following packet will be such an example.
>
> m -> nb_segs=3, pktlen=128, datalen=64
> -> datalen=32
> -> datalen=32
>
>
> It’s unclear if/how we might get into such a multi-segmented pkt
> but I agree we should handle this case. Patch updated taking the
> simple approach (checking for nb_segs == 1). I’ll leave the
> optimization as a future patch.
Such a packet can happen when adding a tunnel header such as VXLAN
and the underlying packet is shared (refcnt > 1) or does not have
enough headroom for the tunnel header.
next prev parent reply other threads:[~2016-01-13 4:50 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-06 0:12 [dpdk-dev] [PATCH v3 0/4] vmxnet3 TSO and tx cksum offload Yong Wang
2016-01-06 0:12 ` [dpdk-dev] [PATCH v3 1/4] vmxnet3: restore tx data ring support Yong Wang
2016-01-06 0:48 ` Stephen Hemminger
2016-01-13 2:20 ` Yong Wang
2016-01-13 4:50 ` Stephen Hemminger [this message]
2016-01-06 0:12 ` [dpdk-dev] [PATCH v3 2/4] vmxnet3: add tx l4 cksum offload Yong Wang
2016-01-06 0:51 ` Stephen Hemminger
2016-01-13 2:20 ` Yong Wang
2016-01-06 0:12 ` [dpdk-dev] [PATCH v3 3/4] vmxnet3: add TSO support Yong Wang
2016-01-06 0:12 ` [dpdk-dev] [PATCH v3 4/4] vmxnet3: announce device offload capability Yong Wang
2016-01-06 0:52 ` Stephen Hemminger
2016-01-13 2:20 ` Yong Wang
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