netdev - Re: small RPS cache for fragments?

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Message-ID: <1305669140.6741.4.camel@edumazet-laptop>
Date:	Tue, 17 May 2011 23:52:20 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: small RPS cache for fragments?

Le mardi 17 mai 2011 à 14:44 -0700, Andi Kleen a écrit :
> Eric Dumazet <eric.dumazet@...il.com> writes:
> >
> > OK but do we have workloads actually needing this optimization at all ?
> 
> That's a good a question.
> >
> > (IP defrag hits a read_lock(&ip4_frags.lock)), so maybe steer all frags
> > on a given cpu ?)
> 
> Couldn't the lock just be replaced with a hashed or bitmap lock or 
> bit in low bits of pointer lock?
> 
> iirc it just protects the heads of the hash table.
> 
> They're not rwlocks, but especially if the locking was more finegrained
> that's likely not needed anymore.

Well, there is the rehashing stuff, and this locks the whole table.

Not easy to switch to rcu or something like that.

Anyway I hardly use frags here at work, so never considered it was a
field to spend time ;)

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