netdev - Re: [PATCH RFC] [INET]: Get cirtical word in first 64bit of cache line

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Date:	Sun, 25 Nov 2012 22:44:01 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	ling.ma.program@...il.com
Cc:	linux-kernel@...r.kernel.org, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH RFC] [INET]: Get cirtical word in first 64bit of cache
 line

On Mon, 2012-11-26 at 11:29 +0800, ling.ma.program@...il.com wrote:
> From: Ma Ling <ling.ma.program@...il.com>
> 
> In order to reduce memory latency when last level cache miss occurs,
> modern CPUs i.e. x86 and arm introduced Critical Word First(CWF) or
> Early Restart(ER) to get data ASAP. For CWF if critical word is first member
> in cache line, memory feed CPU with critical word, then fill others
> data in cache line one by one, otherwise after critical word it must
> cost more cycle to fill the remaining cache line. For Early First CPU will
> restart until critical word in cache line reaches.
> 
> Hash value is critical word, so in this patch we place it as first member
> in cache line(sock address is cache-line aligned), and it is also good for
> Early Restart platform as well .
> 
> Thanks
> Ling

networking patches should be sent to netdev.

(I understand this patch is more a generic one, but at least CC netdev)

You give no performance numbers for this change...

I never heard of this CWF/ER, where are the official Intel documents
about this, and what models really benefit from it ?

Also, why not moving skc_net as well ?

BTW, skc_daddr & skc_rcv_saddr are 'critical' as well, we use them in
INET_MATCH()

It seems we have a 32bit hole on 64bit arches, so we probably should
move inet_dport/inet_num in it. It could well remove a full cache line
miss (I'll send a patch for this after tests)

Thanks




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