netdev - Re: [PATCH v7] rps: Receive Packet Steering

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Message-ID: <412e6f7f1003172348s1f113734h882779d9acd08ddc@mail.gmail.com>
Date:	Thu, 18 Mar 2010 14:48:29 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v7] rps: Receive Packet Steering

On Thu, Mar 18, 2010 at 2:20 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le mercredi 17 mars 2010 à 16:50 -0700, Tom Herbert a écrit :
>>
>> Here is a patch for this...
>>
>> Allow specification of CPUs in rps to be done with a vector instead of a bit map.  This allows relative weighting of CPUs in the map by repeating ones to give higher weight.
>>
>> For example "echo 0 0 0 3 4 4 4 4 > /sys/class/net/eth0/queues/rx-0/rps_cpus"
>>
>> assigns CPUs 0, 3, and 4 to the RPS mask with relative weights 3, 1, and 4 respectively.
>>
>
> Hmm...
>
> I believe we should keep existing sysfs cpumask interface, because its
> the only workable thing on a PAGE_SIZE=4096 machine with 4096 cpus.
>
> strlen("0 1 2 3 4 ... 4095") = 19369
>
> Using base 16 instead of base 10 -> 16111
>

sigh! How about adding file for each cpu weight setting.

.../rx-0/rps_cpu0...n

BTW: I think exporting the hook of hash function will help in some
case. So users can choose which hash to use depend on their
applications. I know FreeBSD supports hash based on flow, source or
CPU. Some network application have multiple instances for taking full
advantage of the SMP/C hardware, and each instance binds to a special
CPU/Core, so they need some kind of load distributing algorithm for
load balancing.

For example, memcached uses hash based on key, and its developer may
implement a hash function for RPS. Then it apply the following
iptables rule:

iptables -A PREROUTING -t nat -m cpu --cpuid 0 -m tcp --dport 1234
--REDIRECT 8081
iptables -A PREROUTING -t nat -m cpu --cpuid 0 -m tcp --dport 1234
--REDIRECT 8082
...

No other things to change, it can take full advantage of the
underlying hardware transparently.

-- 
Regards，
Changli Gao(xiaosuo@...il.com)
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