netdev - Re: [net-next PATCH 3/3] net: frag queue per hash bucket locking

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Date:	Thu, 28 Mar 2013 15:03:59 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	eric.dumazet@...il.com, brouer@...hat.com, netdev@...r.kernel.org,
	fw@...len.de, dborkman@...hat.com
Subject: Re: [net-next PATCH 3/3] net: frag queue per hash bucket locking

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Thu, 28 Mar 2013 19:57:21 +0100

> On Wed, Mar 27, 2013 at 10:25:59AM -0700, Eric Dumazet wrote:
>> On Wed, 2013-03-27 at 16:56 +0100, Jesper Dangaard Brouer wrote:
>> > This patch implements per hash bucket locking for the frag queue
>> > hash.  This removes two write locks, and the only remaining write
>> > lock is for protecting hash rebuild.  This essentially reduce the
>> > readers-writer lock to a rebuild lock.
 ...
>> I am not sure why you added _bh suffix to spin_lock()/spin_unlock()
>> here ?
> 
> I assume that it has to do with the usage of this code in
> ipv6/netfilter/nf_conntrack_reasm.c, which could be invoked from process
> context, if I read it correctly.

That appears to be the case yes.

That's an odd environment for these routines to be invoked from,
so longer term we should probably make the nf conntrack code do
the BH disabling around the inet frag calls, rather than make the
inet frag code eat the extra overhead for the more common invocations.
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