netdev - Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

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Date:	Wed, 7 Nov 2007 13:13:18 +0100
From:	Jarek Poplawski <jarkao2@...pl>
To:	David Miller <davem@...emloft.net>
Cc:	dada1@...mosbay.com, ak@...e.de, netdev@...r.kernel.org,
	acme@...hat.com
Subject: Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

On Wed, Nov 07, 2007 at 02:41:14AM -0800, David Miller wrote:
> From: Eric Dumazet <dada1@...mosbay.com>
> Date: Sun, 04 Nov 2007 12:31:28 +0100
> 
> > [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table
> > 
> > As done two years ago on IP route cache table (commit 
> > 22c047ccbc68fa8f3fa57f0e8f906479a062c426) , we can avoid using one lock per 
> > hash bucket for the huge TCP/DCCP hash tables.
> > 
> > On a typical x86_64 platform, this saves about 2MB or 4MB of ram, for litle 
> > performance differences. (we hit a different cache line for the rwlock, but 
> > then the bucket cache line have a better sharing factor among cpus, since we 
> > dirty it less often). For netstat or ss commands that want a full scan of hash 
> > table, we perform fewer memory accesses.
> > 
> > Using a 'small' table of hashed rwlocks should be more than enough to provide 
> > correct SMP concurrency between different buckets, without using too much 
> > memory. Sizing of this table depends on num_possible_cpus() and various CONFIG 
> > settings.
> > 
> > This patch provides some locking abstraction that may ease a future work using 
> >   a different model for TCP/DCCP table.
> > 
> > Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> > Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> 
> I'm going to push this current version to Linus, the space saving
> really justify it and if we want to refine things further we do it
> with followon work rather than blocking this patch.
> 
> Thanks Eric!

I hope my remarks didn't block anything?! I've written it's OK.
So, I'm not sure it's useful or expected, but anyway:

Acked-by: Jarek Poplawski <jarkao2@...pl>

Thanks,
Jarek P.
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