netdev - Re: [RFC 2/2] udp: udp_lib_get_port start at a different bucket on different processors

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Message-ID: <4B2A3B87.8020603@gmail.com>
Date:	Thu, 17 Dec 2009 15:09:11 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Lucian Adrian Grijincu <lgrijincu@...acom.com>
CC:	netdev@...r.kernel.org, Octavian Purdila <opurdila@...acom.com>
Subject: Re: [RFC 2/2] udp: udp_lib_get_port start at a different bucket on
 different processors

Le 16/12/2009 20:24, Lucian Adrian Grijincu a écrit :
> 
> On SMP, when ports are not allocated randomly, using the same starting
> port on all processors will lead to bad performance as all processors
> will try to get the same hashbucket spinlock: only one will succeed,
> the rest will spin madly.
> 
> We solve this problem by making each processor start searching from a
> different port. To not skip possibly valid port ranges we renormalize
> the hint value too.
> 
> Signed-off-by: Lucian Adrian Grijincu <lgrijincu@...acom.com>
> ---
>  net/ipv4/udp.c |   12 +++++++++---
>  1 files changed, 9 insertions(+), 3 deletions(-)
> 
> 

This makes no sense. You correct a bad performance issue bringed by your previous patch ?

Please submit one patch, with no performance regression.

I suggest you use a per_cpu hint if you really want to be fast...

Thanks
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