From: Hans Westgaard Ry <hans.westgaard.ry@oracle•com>
To: David Laight <David.Laight@ACULAB•COM>,
"David S. Miller" <davem@davemloft•net>
Cc: Alexey Kuznetsov <kuznet@ms2•inr.ac.ru>,
James Morris <jmorris@namei•org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6•org>,
Patrick McHardy <kaber@trash•net>,
Alexei Starovoitov <ast@plumgrid•com>,
Jiri Pirko <jiri@mellanox•com>,
Eric Dumazet <edumazet@google•com>,
Daniel Borkmann <daniel@iogearbox•net>,
Nicolas Dichtel <nicolas.dichtel@6wind•com>,
"Eric W. Biederman " <ebiederm@xmission•com>,
Salam Noureddine <noureddine@arista•com>,
Jarod Wilson <jarod@redhat•com>,
Toshiaki Makita <makita.toshiaki@lab•ntt.co.jp>,
Julian Anastasov <ja@ssi•bg>, Ying Xue <ying.xue@windriver•com>,
Craig Gallek <kraig@google•com>,
Mel Gorman <mgorman@techsingularity•net>,
"\" hannes\"@stressinduktion.org " <hannes@stressinduktion•org>,
Edward Jee <edjee@google•com>,
Julia Lawall <julia.lawall@lip6•fr>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"linux-kernel@vger•kernel.org" <li
Subject: Re: [PATCH] net: add per device sg_max_frags for skb
Date: Fri, 8 Jan 2016 10:55:56 +0100 [thread overview]
Message-ID: <568F87AC.60405@oracle.com> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1CCBE5AA@AcuExch.aculab.com>
On 01/06/2016 02:59 PM, David Laight wrote:
> From: Hans Westgaard Ry
>> Sent: 06 January 2016 13:16
>> Devices may have limits on the number of fragments in an skb they
>> support. Current codebase uses a constant as maximum for number of
>> fragments (MAX_SKB_FRAGS) one skb can hold and use.
>>
>> When enabling scatter/gather and running traffic with many small
>> messages the codebase uses the maximum number of fragments and thereby
>> violates the max for certain devices.
>>
>> An example of such a violation is when running IPoIB on a HCA
>> supporting 16 SGE on an architecture with 4K pagesize. The
>> MAX_SKB_FRAGS will be 17 (64K/4K+1) and because IPoIB adds yet another
>> segment we end up with send_requests with 18 SGE resulting in
>> kernel-panic.
>>
>> The patch allows the device to limit the maximum number fragments used
>> in one skb.
> This doesn't seem to me to be the correct way to fix this.
> Anything that adds an extra fragment (in this case IPoIB) should allow
> for the skb already having the maximum number of fragments.
> Fully linearising the skb is overkill, but I think the first fragment
> can be added to the linear part of the skb.
>
> David
>
>
When IpoIB handles a skb-request it converts fragments to SGEs to
be handled by a HCA.
The problem arises when the HCA have a limited number of SGEs less than
MAX_SKB_FRAGS.
(it gets a little worse since IPoIB need to yet another segment)
I have not found any easy way of fixing this with currenct codebase.
Hans
next prev parent reply other threads:[~2016-01-08 9:55 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-01-06 13:16 [PATCH] net: add per device sg_max_frags for skb Hans Westgaard Ry
2016-01-06 13:59 ` David Laight
2016-01-08 9:55 ` Hans Westgaard Ry [this message]
2016-01-08 10:33 ` David Laight
2016-01-08 11:47 ` Hannes Frederic Sowa
2016-01-13 13:57 ` Hans Westgaard Ry
2016-01-13 14:19 ` Eric Dumazet
2016-01-13 14:20 ` Eric Dumazet
2016-01-13 15:07 ` Hannes Frederic Sowa
2016-01-13 15:38 ` David Miller
2016-01-13 15:44 ` Eric Dumazet
2016-01-13 21:07 ` Eric W. Biederman
2016-01-27 13:20 ` [PATCH v2] net:Add sysctl_tcp_sg_max_skb_frags Hans Westgaard Ry
2016-01-27 15:15 ` Eric Dumazet
2016-01-27 18:12 ` Hannes Frederic Sowa
2016-02-01 13:12 ` Hans Westgaard Ry
2016-01-27 20:13 ` David Miller
2016-02-03 8:26 ` [PATCH v3] net:Add sysctl_max_skb_frags Hans Westgaard Ry
2016-02-03 11:25 ` Herbert Xu
2016-02-03 11:36 ` Hannes Frederic Sowa
2016-02-03 12:20 ` Herbert Xu
2016-02-03 14:03 ` Hannes Frederic Sowa
2016-02-03 14:30 ` Eric Dumazet
2016-02-03 17:36 ` David Laight
2016-02-03 15:58 ` Alexander Duyck
2016-02-03 16:07 ` Eric Dumazet
2016-02-03 17:43 ` Alexander Duyck
2016-02-03 17:54 ` Eric Dumazet
2016-02-03 18:24 ` Alexander Duyck
2016-02-03 19:23 ` Eric Dumazet
2016-02-03 21:03 ` Alexander Duyck
2016-02-09 9:30 ` David Miller
2016-01-06 14:05 ` [PATCH] net: add per device sg_max_frags for skb Eric Dumazet
2016-01-08 10:01 ` Hans Westgaard Ry
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