netdev - Re: [RFC PATCH] net, rps: bypass enqueue_to

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Message-ID: <CAEH94LiX640J_L+ZACj8d5g3xVygUPT-K2_MFOj8-w6S3G=hUQ@mail.gmail.com>
Date:	Wed, 18 Dec 2013 22:20:48 +0800
From:	Zhi Yong Wu <zwu.kernel@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Tom Herbert <therbert@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH] net, rps: bypass enqueue_to_backlog()

thanks for your explanation.

by the way, pls ignore this patch, thanks.

On Wed, Dec 18, 2013 at 9:56 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2013-12-18 at 21:03 +0800, Zhi Yong Wu wrote:
>> From: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>>
>> When local cpu is just target cpu which will handle network soft irq,
>> the packet should be directly injected to network stack, by bypassing
>> enqueue_to_backlog(), it can speed up the packet processing.
>>
>> HI, guys
>>
>> I checked the first several versions of RPS patch which seemed to have
>> this condition determination, but why was it removed later? Do i miss
>> anything? if yes, please correct me, thanks.
>>
>> Signed-off-by: Zhi Yong Wu <wuzhy@...ux.vnet.ibm.com>
>> ---
>
> Hmm... Could you elaborate ?
>
> At which point do you think this condition was tested or removed ?
>
> I think the idea was to drain NIC RX queues as fast as possible, then :
>
> - Send the IPI to remote cpus
> - process our queue in parallel with other cpus processing their own
> queue.
>
> If we process our packets through whole stack, packets for other cpus
> will have a fair amount of extra latency.
>
> Thats a tradeoff I suppose.
>
>



-- 
Regards,

Zhi Yong Wu
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