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From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: Olivier Matz <olivier.matz@6wind.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	"Richardson, Bruce" <bruce.richardson@intel.com>,
	Adrien Mazarguil <adrien.mazarguil@6wind.com>,
	"Tan, Jianfeng" <jianfeng.tan@intel.com>
Subject: Re: [dpdk-dev] about rx checksum flags
Date: Tue, 31 May 2016 16:09:16 +0800	[thread overview]
Message-ID: <20160531080916.GI5641@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <574C5B9D.4080006@6wind.com>

On Mon, May 30, 2016 at 05:26:21PM +0200, Olivier Matz wrote:
> Hi,
> 
> I'm planning to add the support for offloads in virtio-net pmd.

Good to know, and thanks!

> It appears that the current rx flags in mbuf are not sufficient to
> describe the state of a packet received from a virtual driver.
> I think we need a way to say "the checksum in the packet data is
> not calculated, but the integrity of the data is verified".
> 
> Currently, we have one flag for L4 (same for IP):
> 
>   PKT_RX_L4_CKSUM_BAD: L4 cksum of RX pkt. is not OK.
> 
> This has also another problem that has already been discussed [1]:
> if no flag is set, it is expected that the checksum is verified by
> hw, but there is no way to say "the hw does not know if the cksum
> is correct".
> 
> I would like to extend this flag to a 4-state value (2 bits):
> 
>  PKT_RX_L4_CKSUM_UNKNOWN: no information about the RX L4 checksum
>   -> the application should verify the checksum by sw
> 
>  PKT_RX_L4_CKSUM_BAD: the L4 checksum in the packet is wrong
>   -> the application can drop the packet without additional check
> 
>  PKT_RX_L4_CKSUM_GOOD: the L4 checksum in the packet is valid
>   -> the application can accept the packet without verifying the
>      checksum by sw

This is good to have, which could save some burderns of cksum
validation when using kernel virtio-net (that has a TCP/IP stack
on top of it) and vhost-user combo.

> 
>  PKT_RX_L4_CKSUM_NONE: the L4 checksum is not correct in the packet
>  data, but the integrity of the L4 header is verified.
>   -> the application can process the packet but must not verify the
>      checksum by sw. It has to take care to recalculate the cksum
>      if the packet is transmitted (either by sw or using tx offload)

I like the explanation you made at [1] better :)

So in general, I think this proposal is good to have.

	--yliu

> To keep the compatibility with application, the old flag is kept at the
> same value, and a new flag is added. It is assumed that the behavior
> of applications was:
> 
>   PKT_RX_L4_CKSUM_BAD = 0 -> packet is accepted
>   PKT_RX_L4_CKSUM_BAD = 1 -> packet is dropped
> 
> The new checksum states for L4 (same for IP) would be:
> 
>   old flag   new flag   meaning
>   0          0          PKT_RX_L4_CKSUM_UNKNOWN
>   1          0          PKT_RX_L4_CKSUM_BAD
>   0          1          PKT_RX_L4_CKSUM_GOOD
>   1          1          PKT_RX_L4_CKSUM_NONE
> 
> With this, an old application that only checks the old flag, and
> running using a dpdk having this modification would accept GOOD and
> UNKNOWN packets (like today), drop BAD packets (like today) and
> drop NONE packets (this is a new feature that has to be explicitly
> enabled by the application).
> 
> 
> Any comment?
> 
> Olivier
> 
> 
> [1] http://dpdk.org/ml/archives/dev/2015-January/011550.html

  parent reply	other threads:[~2016-05-31  8:06 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-30 15:26 Olivier Matz
2016-05-30 16:07 ` Adrien Mazarguil
2016-05-31  2:43 ` Tan, Jianfeng
2016-05-31 10:08   ` Adrien Mazarguil
2016-05-31 19:11     ` Olivier MATZ
2016-05-31  8:09 ` Yuanhan Liu [this message]
2016-05-31 19:11   ` Olivier MATZ
2016-05-31 20:28     ` Stephen Hemminger
2016-05-31 20:58       ` Olivier MATZ
2016-05-31 22:02         ` Stephen Hemminger
2016-06-01  9:06           ` Ananyev, Konstantin
2016-06-02  7:42             ` Chandran, Sugesh
2016-06-03 12:43               ` Olivier Matz
2016-06-08  8:22                 ` Chandran, Sugesh
2016-06-08 13:02                   ` Olivier Matz
2016-06-10 16:15                     ` Chandran, Sugesh
2016-07-06 12:52                       ` Chandran, Sugesh
2016-07-06 13:18                         ` Olivier MATZ

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