Date: Fri, 9 Nov 2012 09:51:47 +0100 From: Fabien Thomas <fabien.thomas@netasq.com> To: Alexander V. Chernikov <melifaro@FreeBSD.org> Cc: freebsd-net@FreeBSD.org, Andre Oppermann <oppermann@networx.ch>, freebsd-hackers@FreeBSD.org Subject: Re: [patch] reducing arp locking Message-ID: <49EE4F42-6162-40F4-9DE0-1ACA1289B225@netasq.com> In-Reply-To: <509B88B1.3070905@FreeBSD.org> References: <509AEDAC.10002@FreeBSD.org> <509B884F.7040106@networx.ch> <509B88B1.3070905@FreeBSD.org>
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Le 8 nov. 2012 à 11:25, Alexander V. Chernikov a écrit : > 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. How do you protect from entry update if i've a ref to the entry ? You can end up doing bcopy of a partial mac address. la_preempt modification is also write access to an unlocked structure. > >> 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 > > > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org"
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