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@gmail.com wrote:

From: Ma Ling <redacted>

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