linux-kernel - Re: [PATCH 1/2] ehea: fix delayed packet processing

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Date:	Tue, 15 Jun 2010 09:45:47 -0700
From:	Jay Vosburgh <fubar@...ibm.com>
To:	"Jan-Bernd Themann" <ossthema@...ibm.com>
cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	tklein@...ux.ibm.com, Andre Detsch <adetsch@...ibm.com>,
	themann@...ibm.com
Subject: Re: [PATCH 1/2] ehea: fix delayed packet processing

Jan-Bernd Themann <ossthema@...ibm.com> wrote:

>In the eHEA poll function an rmb() is required. Without that some packets
>on the receive queue are not seen and thus delayed until the next interrupt
>is handled for the same receive queue.
>
>Signed-off-by: Jan-Bernd Themann <themann@...ibm.com>

	To add a bit of background, this could manifest during a netperf
TCP_RR or UDP_RR on an otherwise idle network.  TCP would occasionally
retransmit, but then both the original segment and the retransmission
would simultaneously appear at the receiver.  For UDP_RR, message sizes
in excess of the mtu would occasionally "lose" an IP fragment, and
eventually IP reassembly would time out.

	-J

Signed-off-by: Jay Vosburgh <fubar@...ibm.com>


>---
>Patch created against 2.6.35-rc3
>
> drivers/net/ehea/ehea_main.c |    1 +
> 1 files changed, 1 insertions(+), 0 deletions(-)
>
>diff --git a/drivers/net/ehea/ehea_main.c b/drivers/net/ehea/ehea_main.c
>index f547894..fd890fa 100644
>--- a/drivers/net/ehea/ehea_main.c
>+++ b/drivers/net/ehea/ehea_main.c
>@@ -867,6 +867,7 @@ static int ehea_poll(struct napi_struct *napi, int budget)
> 		ehea_reset_cq_ep(pr->send_cq);
> 		ehea_reset_cq_n1(pr->recv_cq);
> 		ehea_reset_cq_n1(pr->send_cq);
>+		rmb();
> 		cqe = ehea_poll_rq1(pr->qp, &wqe_index);
> 		cqe_skb = ehea_poll_cq(pr->send_cq);
>
>-- 
>1.7.0
>--
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