[dpdk-users] i40e vPMD fix out of order Rx read issue

Zhang, Qi Z qi.z.zhang at intel.com
Thu Jul 25 14:11:01 CEST 2019

Hi Gavin:

	in vPMD, we read 4 or 8 packets as batch, we count DD bits for packet received, but not check the if they are continues or not, we assume it should always be 1000, 1100, 1110, 1111 ....(take batch size is 4 as example)
	while the out of order read instruction generated by compiler will cause driver to get un-continues DD bits, like 1011, the descriptor on the hole actually is invalid since when it is read , descriptor is not write back yet, but we still process this as 1110, it cause an corrupted mbuf returned.
	hope this is helpful.


> -----Original Message-----
> From: Gavin Hu (Arm Technology China) [mailto:Gavin.Hu at arm.com]
> Sent: Thursday, July 25, 2019 5:57 PM
> To: Zhang, Qi Z <qi.z.zhang at intel.com>; Richardson, Bruce
> <bruce.richardson at intel.com>; Ananyev, Konstantin
> <konstantin.ananyev at intel.com>
> Cc: users at dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli at arm.com>; Phil Yang (Arm Technology China)
> <Phil.Yang at arm.com>
> Subject: i40e vPMD fix out of order Rx read issue
> Hi Qi,
> I am working on optimizing the i40e vPMD on aarch64 and I see this patch
> relevant.
> Could you illuminate what issue this patch was fixing?
> I understand the PMD works at the driver layer, for delivery of L2 packets.
> It does not own the responsibility to keep order(the responsibility lies with the
> protocol stack, like TCP)?
> http://patches.dpdk.org/patch/16665/
> Best regards,
> Gavin
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