netdev - Re: [net-next PATCH 0/4] net: frag patchset for fixing LRU scalability issue

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Date:	Wed, 24 Apr 2013 19:27:03 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [net-next PATCH 0/4] net: frag patchset for fixing LRU scalability issue

On Wed, Apr 24, 2013 at 05:47:55PM +0200, Jesper Dangaard Brouer wrote:
> This patchset replaces my prevous patchset:
>   "net: frag code fixes and RFC for LRU removal"
>   http://thread.gmane.org/gmane.linux.network/266323/
> 
> I have dropped the idea of doing "direct hash cleaning".  Instead I
> have simply choosen to solve the global LRU list problem, by making
> the LRU list be per CPU.
> 
> 
> Patch-01: Revert "inet: limit length of fragment queue hash table bucket lists"
> - Sorry this patch is broken and need to be reverted.
>   I'll leave it up to Hannes for come up with a better solution,
>   perhaps better IPv6 hashing for frag queues.

In general I am fine with this approach. I will have a look if we can
mitigate the IPv6 hash collisions without reverting 279e9f2 ("ipv6:
optimize inet6_hash_frag()") ontop of this patchset. I will send a patch
if these changes land in net-next.

> Patch-02: net: increase frag hash size
> - Simply increase the hash size
> 
> Patch-03: net: avoid false perf interpretations in frag code
> - The compiler make us misinterpret performance issues in the frag
>   code, because its auto inlining functions.  This cause too many
>   arguments between developers on the list.
> 
> Patch-04: net: frag LRU list per CPU
> - Change the global LRU list to be per CPU instead.

I will review the other patches later today. Btw. do we have to deal
with online cpu-addition/removal here?

Thanks,

  Hannes

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