netdev - Re: rps perfomance WAS(Re: rps: question

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Date:	Fri, 16 Apr 2010 22:58:12 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	hadi@...erus.ca
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>, therbert@...gle.com,
	netdev@...r.kernel.org, robert@...julf.net, andi@...stfloor.org
Subject: Re: rps perfomance WAS(Re: rps: question

On Fri, Apr 16, 2010 at 10:43 PM, jamal <hadi@...erus.ca> wrote:
> On Fri, 2010-04-16 at 22:10 +0800, Changli Gao wrote:
>> On Fri, Apr 16, 2010 at 9:49 PM, jamal <hadi@...erus.ca> wrote:
>
>> > my observation is:
>> > s->total is the sum of all packets received by cpu (some directly from
>> > ethernet)
>>
>> It is meaningless currently. If rps is enabled, it may be twice of the
>> number of the packets received, because one packet may be count twice:
>> one in enqueue_to_backlog(), and the other in __netif_receive_skb().
>
> You are probably right - you made me look at my collected data ;->
> i will look closely later, but it seems they are accounting for
> different cpus, no?
> Example, attached are some of the stats i captured when i was running
> the tests redirecting from CPU0 to CPU1 1M packets at about 20Kpps (just
> cut to the first and last two columns):
>
> cpu   Total     |rps_recv |rps_ipi
> -----+----------+---------+---------
> cpu0 | 002dc7f1 |00000000 |000f4246
> cpu1 | 002dc804 |000f4240 |00000000
> -------------------------------------
>
> So: cpu0 receive 0x2dc7f1 pkts accummulative over time and
> redirected to cpu1 (mostly, the extra 5 maybe to leftover since i clear
> the data) and for the test 0xf4246 times it generated an IPI. It can be
> seen that total running for CPU1 is 0x2dc804 but in this one run it
> received 1M packets (0xf4240).

I remeber you redirected all the traffic from cpu0 to cpu1, and the data shows:

about 0x2dc7f1 packets are processed, and about 0xf4240 IPI are generated.

> i.e i dont see the double accounting..
>

a single packet is counted twice by CPU0 and CPU1. If you change RPS setting by:

echo 1 > ..../rps_cpus

you will find the total number are doubled.


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