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Date: Thu, 08 Nov 2012 14:25:53 +0400
From: "Alexander V. Chernikov" <melifaro@FreeBSD.org>
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To: Andre Oppermann <oppermann@networx.ch>
Subject: Re: [patch] reducing arp locking
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On 08.11.2012 14:24, Andre Oppermann wrote:
> On 08.11.2012 00:24, Alexander V. Chernikov wrote:
>> Hello list!
>>
>> Currently we need to acquire 2 read locks to perform simple 6-byte
>> copying from arp record to packet
>> ethernet header.
>>
>> It seems that acquiring lle lock for fast path (main traffic flow) is
>> not necessary even with
>> current code.
>>
>> My tests shows ~10% improvement with this patch applied.
>>
>> If nobody objects I plan to commit this change at the end of next week.
>
> This is risky and prone to race conditions.  The copy of the MAC address
> should be done while the table read lock is held to protect against the
It is done exactly as you say: table read lock is held.

> entry going away.  You can either return with table lock held and drop
> it after the copy, or you could a modified lookup function that takes a
> pointer for the copy destination, do the copy with the read lock, and then
> return.  If no entry is found an error is returned and obviously no copy
> is done.
>


-- 
WBR, Alexander