netdev - Re: [PATCH v4 1/1] rps: core implementation

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Message-ID: <4B0736EB.8090406@gmail.com>
Date:	Sat, 21 Nov 2009 01:40:11 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Tom Herbert <therbert@...gle.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH v4 1/1] rps: core implementation

Tom Herbert wrote, On 11/21/2009 01:12 AM:

>> I guess my confusion is from the:
>>
>>                                __raise_softirq_irqoff(NET_RX_SOFTIRQ);
>>
>> you are doing as you set the cpus in rps_remote_softirq_cpus.
>>
>> Why do you need to schedule the local RX softirq, when we know we're
>> in a NAPI poll loop and thus that we're in a softirq, and thus that we
>> will fire off the IPIs at the end of net_rx_action()?
>>
>> That's what you're doing, the softirq raising just seems superfluous.
>>
> 
> Ah, right. If RPS can't be used non-NAPI case, this line is now
> superfluous.  It can be removed.

Hmm... mostly right. At least if it's wrt. my previous opinion. I meant
only that non-NAPI case would be handled less optimally without this
dedicated softirq, but __raise_softirq_irqoff(NET_RX_SOFTIRQ) or
napi_schedule(&queue->backlog) could be called from netif_rx().

Jarek P.
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