From: Eric Dumazet <dada1@cosmosbay•com>
To: David Miller <davem@davemloft•net>
Cc: netdev@vger•kernel.org
Subject: Re: [RFC] net: release dst entry in dev_queue_xmit()
Date: Wed, 25 Mar 2009 08:13:30 +0100 [thread overview]
Message-ID: <49C9D99A.2040900@cosmosbay.com> (raw)
In-Reply-To: <20090324.234354.43714160.davem@davemloft.net>
David Miller a écrit :
> From: Eric Dumazet <dada1@cosmosbay•com>
> Date: Fri, 20 Mar 2009 12:40:22 +0100
>
>> I believe we can release dst in dev_queue_xmit(), while cpu cache is
>> hot, since caller of dev_queue_xmit() had to hold a reference on dst
>> right before. This reduce work to be done by softirq handler, and
>> decrease cache misses.
>>
>
> This will break various packet schedulers and classifiers.
>
> Heck sch_sfq.c even uses skb->dst as part of it's flow hash
> function :-)
Well, as one of the hash perturbator, for other protocols than
IPV4 & IPV6...
default:
h = (unsigned long)skb->dst ^ skb->protocol;
h2 = (unsigned long)skb->sk;
}
return sfq_fold_hash(q, h, h2);
But teql indeed mandates dst in __teql_resolve()
Darn...
This dst freeing should be done very late then, in the NIC driver itself, just
before giving skb to hardware, or right before in dev_hard_start_xmit()
If done in dev_hard_start_xmit(), skb could be requeued (because of NETDEV_TX_BUSY).
Then if requeued, maybe at this time, dst being NULL is not a problem ?
Thanks a lot David
next prev parent reply other threads:[~2009-03-25 7:13 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-20 11:40 [RFC] net: release dst entry in dev_queue_xmit() Eric Dumazet
2009-03-20 14:10 ` Neil Horman
2009-03-25 6:43 ` David Miller
2009-03-25 7:13 ` Eric Dumazet [this message]
2009-03-25 7:17 ` David Miller
2009-03-25 18:22 ` Jarek Poplawski
2009-03-25 18:41 ` Eric Dumazet
2009-03-25 19:18 ` Jarek Poplawski
2009-03-25 19:40 ` Eric Dumazet
2009-03-25 19:54 ` Jarek Poplawski
2009-03-25 20:28 ` Eric Dumazet
2009-03-25 21:12 ` Jarek Poplawski
2009-03-25 21:20 ` Patrick McHardy
2009-05-12 8:12 ` [PATCH] net: release dst entry in dev_hard_start_xmit() Eric Dumazet
2009-05-12 8:21 ` Eric Dumazet
2009-05-12 19:26 ` [PATCH, v2] " Eric Dumazet
2009-05-19 5:19 ` David Miller
2009-05-19 5:44 ` Eric Dumazet
2009-05-19 19:44 ` Eric Dumazet
2009-05-19 21:09 ` Jarek Poplawski
2009-05-19 21:21 ` Eric Dumazet
2009-05-19 21:24 ` David Miller
2009-05-12 19:27 ` [PATCH] " Jarek Poplawski
2009-05-12 19:44 ` Eric Dumazet
2009-05-12 20:05 ` Jarek Poplawski
2009-05-12 20:24 ` Jarek Poplawski
2009-05-12 20:52 ` Eric Dumazet
2009-05-12 20:59 ` Jarek Poplawski
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