netdev - Re: RPS will assign different smp_processor

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Message-ID: <BANLkTi=gTNwKX1Tb3mqgWJekRf7n_MHpJQ@mail.gmail.com>
Date:	Fri, 22 Apr 2011 00:29:45 +0800
From:	zhou rui <zhourui.cn@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: RPS will assign different smp_processor_id for the same packet?

On Friday, April 22, 2011, Eric Dumazet <eric.dumazet@...il.com> wrote:
> Le jeudi 21 avril 2011 à 18:08 +0200, Eric Dumazet a écrit :
>> Le jeudi 21 avril 2011 à 23:50 +0800, zhou rui a écrit :
>> > kernel 2.6.36.4
>> > CONFIG_RPS=y but not set the cpu mask
>> >
>> > /sys/class/net/eth1/queues/rx-0 # cat rps_cpus
>> > 00
>> >
>> > register a hook func:
>> >   prot_hook.func = packet_rcv;
>> >   prot_hook.type = htons(ETH_P_ALL);
>> >   dev_add_pack(&prot_hook);
>> >
>> >
>> > replay the same traffic in very slow speed, printk the
>> > smp_processor_id in packet_rcv():
>> > first time:
>> > cpu=4
>> > cpu=3
>> > cpu=6
>> > cpu=7
>> >
>> > second time:
>> > cpu=7
>> > cpu=1
>> > cpu=5
>> > cpu=2
>> >
>> > is it normal?
>>
>> Yes it is.
>>
>> What would you expect ?
>>
>
> If rps_cpus contains only '0' bits, it basically means RPS is not active
> for this input queue.
>
> CPU is therefore not changed : The cpu handling NAPI on your network
> device directly calls upper linux stack.
>
> Seeing your traces, it also means your device spreads its interrupts on
> many different cpus, this might be not optimal.
>
> Check /proc/irq/{irq_number}/smp_affinity, it probably contains "ff"
>
>
>
>
Thanks,just saw this email
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