netdev - Re: [PATCH v2 net-next 7/8] net: reorganize struct sock for better data locality

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Date:   Mon, 05 Dec 2016 13:36:24 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net-next 7/8] net: reorganize struct sock for better
 data locality

Hi Eric,

On Sat, 2016-12-03 at 11:14 -0800, Eric Dumazet wrote:
> Group fields used in TX path, and keep some cache lines mostly read
> to permit sharing among cpus.
> 
> Gained two 4 bytes holes on 64bit arches.
> 
> Added a place holder for tcp tsq_flags, next to sk_wmem_alloc
> to speed up tcp_wfree() in the following patch.
> 
> I have not added ____cacheline_aligned_in_smp, this might be done later.
> I prefer doing this once inet and tcp/udp sockets reorg is also done.
> 
> Tested with both TCP and UDP.
> 
> UDP receiver performance under flood increased by ~20 % :
> Accessing sk_filter/sk_wq/sk_napi_id no longer stalls because sk_drops
> was moved away from a critical cache line, now mostly read and shared.

I cherry-picked this patch only for some UDP benchmark. Under flood with
many concurrent flows, I see this 20% improvement and a relevant
decrease in system load.

Nice work, thanks Eric!

Tested-by: Paolo Abeni <pabeni@...hat.com>