From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Olivier Matz <olivier.matz@6wind.com>
Cc: dev@dpdk.org, maxime.coquelin@redhat.com, huawei.xie@intel.com,
stephen@networkplumber.org, "Tan,
Jianfeng" <jianfeng.tan@intel.com>,
Tomasz Kulasek <tomaszx.kulasek@intel.com>,
Thomas Monjalon <thomas.monjalon@6wind.com>,
Konstantin Ananyev <konstantin.ananyev@intel.com>
Subject: Re: [dpdk-dev] [PATCH 5/5] net/virtio: fix Tso when mbuf is shared
Date: Mon, 16 Jan 2017 14:48:19 +0800 [thread overview]
Message-ID: <20170116064819.GL9770@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <20170109184625.7884290a@platinum>
On Mon, Jan 09, 2017 at 06:46:25PM +0100, Olivier Matz wrote:
> The virtio specifications requires that the L4 checksum is set to the
> pseudo header checksum. You can search for "pseudo header" in the
> following doc:
> http://docs.oasis-open.org/virtio/virtio/v1.0/cs04/virtio-v1.0-cs04.pdf
>
> Especially in 5.1.6.2.1, we can see that if we use the csum flag, we
> must set the checksum to phdr, and if we do tso, we must set the csum
> flag.
>
> We can check that this is really needed with Linux vhost by replaying
> the test plan described at [1].
>
> [1] http://dpdk.org/ml/archives/dev/2016-October/048793.html
>
> If we add the following patch to disable the checksum fix (on top of
> this patchset), the test1 "large packets (lro/tso)" won't work.
>
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -224,6 +224,9 @@
> uint32_t tmp;
> int shared = 0;
>
> + if (1)
> + return 0;
> +
> /* mbuf is write-only, we need to copy the headers in a linear
> buffer */ if (unlikely(rte_pktmbuf_data_is_shared(m, 0, hdrlen))) {
> shared = 1;
>
>
> In one direction ("flow1" in the test desc), large packets are
> transmitted from host on the ixgbe interface, and received by the
> guest. Then, testpmd bridges the packet to the virtio interface. But
> the packet is not received by the host.
I hope I could have time to dig this further, since, honestly, I don't
quite like this patch: it makes things un-maintainable.
Besides that, I think we have similar issue with nic drivers. See the
rte_net_intel_cksum_flags_prepare() function introduced at commit
4fb7e803eb1a ("ethdev: add Tx preparation").
Cc more people here. And here is a quick background for them: NIC drivers
doing TSO need change the mbuf (say, for cksum updating), however, as
Stephen pointed out, we could not do that if the mbuf is shared: I don't
see such checks in the driver code as well.
> There are at least 2 options for this one:
>
> - try to use 2 different descriptors (the patch is probably harder,
> and it may slow-down the case where ANY_LAYOUT is supported)
>
> - refuse to initialize with TSO enabled if ANY_LAYOUT is not supported.
>
> If you think ANY_LAYOUT is most likely true today, we could choose
> option 2. Let me know what's your preference here.
Maybe we could go with a simpler one: COW. Yeah, it costs more, but this
would be rare, that it should be OKay, right? Besides, we just need copy
the heading mbuf.
--yliu
next prev parent reply other threads:[~2017-01-16 6:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-24 8:56 [dpdk-dev] [PATCH 0/5] virtio/mbuf: fix virtio tso with shared mbufs Olivier Matz
2016-11-24 8:56 ` [dpdk-dev] [PATCH 1/5] mbuf: remove const attribute in mbuf read function Olivier Matz
2016-11-24 8:56 ` [dpdk-dev] [PATCH 2/5] mbuf: new helper to check if a mbuf is shared Olivier Matz
2016-11-24 8:56 ` [dpdk-dev] [PATCH 3/5] mbuf: new helper to write data in a mbuf chain Olivier Matz
2016-11-24 8:56 ` [dpdk-dev] [PATCH 4/5] mbuf: new helper to copy data from a mbuf Olivier Matz
2016-11-24 8:56 ` [dpdk-dev] [PATCH 5/5] net/virtio: fix Tso when mbuf is shared Olivier Matz
2016-12-14 7:27 ` Yuanhan Liu
2017-01-09 17:46 ` Olivier Matz
2017-01-16 6:48 ` Yuanhan Liu [this message]
2017-01-17 11:18 ` Olivier Matz
2017-01-18 5:03 ` Yuanhan Liu
2017-01-24 10:51 ` Olivier MATZ
2017-01-28 12:32 ` Yuanhan Liu
2017-01-09 17:59 ` Stephen Hemminger
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