netdev - Re: [PATCH] rps: add flow director support

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Date:	Mon, 12 Apr 2010 22:27:04 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Tom Herbert <therbert@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] rps: add flow director support

On Mon, Apr 12, 2010 at 9:34 PM, Tom Herbert <therbert@...gle.com> wrote:
> On Sun, Apr 11, 2010 at 2:42 PM, Changli Gao <xiaosuo@...il.com> wrote:
>> add rps flow director support
>>
>> with rps flow director, users can do weighted packet dispatching among CPUs.
>> For example, CPU0:CPU1 is 1:3 for eth0's rx-0:
>>
> "Flow director" is a misnomer here in that it has no per flow
> awareness, that is what RFS provides.  Please use a different name.

Flow here is a bundle of flow, not the original meaning. How about
"rps_buckets" and "rps_bucket_x"?

>
>>  localhost linux # echo 4 > /sys/class/net/eth0/queues/rx-0/rps_flows
>>  localhost linux # echo 0 > /sys/class/net/eth0/queues/rx-0/rps_flow_0
>>  localhost linux # echo 1 > /sys/class/net/eth0/queues/rx-0/rps_flow_1
>>  localhost linux # echo 1 > /sys/class/net/eth0/queues/rx-0/rps_flow_2
>>  localhost linux # echo 1 > /sys/class/net/eth0/queues/rx-0/rps_flow_3
>>
> It might be better to put this in its own directory

I have thought that before, but since they control the same data in
kernel as rps_cpus does, I put them in the same directory.

> and also do it per
> CPU instead of hash entry.  This should result in a lot fewer entries
> and I'm not sure how you would deal with holes in the hash table for
> unspecified entries.  Also, it would be nice not to have to specify a
> number of entries.  Maybe something like:
>
> localhost linux # echo 1 > /sys/class/net/eth0/queues/rx-0/rps_cpu_map/0
> localhost linux # echo 3 > /sys/class/net/eth0/queues/rx-0/rps_cpu_map/1
>
> To specify CPU 0 with weight 1, CPU 1 with weight 3.
>

Your way is more simple and straightforward. My idea has it own advantage:
1. control the rate precision through rps_flows.
2. do dynamic weighted packet dispatching by migrating some flows from
some CPUs to other CPUs. During this operations, only the flows
migrated are affected, and OOO only occurs in these flows.

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