netdev - Re: [PATCH] udp: avoid searching when no ports are available

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Date:	Fri, 25 Feb 2011 17:55:17 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Daniel Baluta <dbaluta@...acom.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	Rohan Chitradurga <rohan@...acom.com>
Subject: Re: [PATCH] udp: avoid searching when no ports are available

Le vendredi 25 février 2011 à 18:45 +0200, Daniel Baluta a écrit :
> I guess now, the correct bitmap size is MAX_UDP_PORTS / (udptable->mask + 1)
> or  MAX_UDP_PORTS >> udptable->log,  right?
> 


Yes, but using bitmap_zero(bitmap, PORTS_PER_CHAIN) is faster.

It generates 4 machine instructions,
	movq   $0x0,(%r10)
	movq   $0x0,0x8(%r10)
	movq   $0x0,0x10(%r10)
	movq   $0x0,0x18(%r10)

while bitmap_zero(bitmap, some_non_constant_expression) is more
expensive (it calls an out of line function)


> We don't have special needs on a small machine. We just want that when
> when all UDP ports are exhausted, bind calls to fail faster.
> 
> I will be back with tests on latest kernel.

Hmm, please always use the latest kernel before sending patches.

Thanks


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