netdev - Re: [PATCH] bnx2x: fix panic when TX ring is full

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Message-ID: <CA+yapKM+H0DHA_UotD7v5LRZfYUeanupxb4=r89+fVSTo-Ad4w@mail.gmail.com>
Date:	Mon, 18 Jun 2012 10:18:59 -0700
From:	Tomas Hruby <thruby@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Dmitry Kravkov <dmitry@...adcom.com>,
	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"therbert@...gle.com" <therbert@...gle.com>,
	"evansr@...gle.com" <evansr@...gle.com>,
	Eilon Greenstein <eilong@...adcom.com>,
	Merav Sicron <meravs@...adcom.com>,
	Yaniv Rosner <yaniv.rosner@...adcom.com>,
	"willemb@...gle.com" <willemb@...gle.com>
Subject: Re: [PATCH] bnx2x: fix panic when TX ring is full

On Mon, Jun 18, 2012 at 12:38 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Sat, 2012-06-16 at 07:40 +0000, Dmitry Kravkov wrote:
>> Hi Eric and Tomas
>>
>> > From: netdev-owner@...r.kernel.org [mailto:netdev-
>> > owner@...r.kernel.org] On Behalf Of David Miller
>> > Sent: Saturday, June 16, 2012 1:31 AM
>> > To: eric.dumazet@...il.com
>> > Cc: netdev@...r.kernel.org; therbert@...gle.com; evansr@...gle.com;
>> > Eilon Greenstein; Merav Sicron; Yaniv Rosner; willemb@...gle.com;
>> > thruby@...gle.com
>> > Subject: Re: [PATCH] bnx2x: fix panic when TX ring is full
>> >
>> > From: Eric Dumazet <eric.dumazet@...il.com>
>> > Date: Wed, 13 Jun 2012 21:45:16 +0200
>> >
>> > > From: Eric Dumazet <edumazet@...gle.com>
>> > >
>> > > There is a off by one error in the minimal number of BD in
>> > > bnx2x_start_xmit() and bnx2x_tx_int() before stopping/resuming tx
>> > queue.
>> > >
>> > > A full size GSO packet, with data included in skb->head really needs
>> > > (MAX_SKB_FRAGS + 4) BDs, because of bnx2x_tx_split()
>> > >
>> > > This error triggers if BQL is disabled and heavy TCP transmit traffic
>> > > occurs.
>> > >
>> > > bnx2x_tx_split() definitely can be called, remove a wrong comment.
>> > >
>> > > Reported-by: Tomas Hruby <thruby@...gle.com>
>> > > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
>>
>> Theoretically a can't see how we can reach the case with 4 BDs required apart of frags,
>> Usually we need 2, when split invoked 3:
>> 1.Start
>> 2.Start(split)
>> 3.Parsing
>> + Frags
>>
>> Next pages descriptors and 2 extras for full indication are not counted as available.
>>
>> Practically I'm running the traffic for more then a day without hitting the panic.
>>
>> Can you describe the scenario you reproduced this in details? And which code has paniced?
>
> Thats pretty immediate.

yes

> Disable bql on your NIC.
>
> Say you have 4 queues :
>
> for q in 0 1 2 3
> do
>  echo max >/sys/class/net/eth0/queues/tx-$q/byte_queue_limits/limit_min
> done
>
> Then start 40 netperf
>
> for i in `seq 1 40`
> do
>  netperf -H 192.168.1.4 &
> done

this is enough in my case too, it is perfectly reproducible on
different machines. Replacing +3 for +4 fixes the problem.

T.
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