netdev - Re: [PATCH RFC net-next] net: epoll support for busy poll

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Date:	Wed, 21 Aug 2013 18:09:06 +0300
From:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, e1000-devel@...ts.sourceforge.net,
	Eilon Greenstein <eilong@...adcom.com>,
	Amir Vadai <amirv@...lanox.com>,
	Willem de Bruijn <willemb@...gle.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH RFC net-next] net: epoll support for busy poll

On 21/08/2013 16:53, Eric Dumazet wrote:
> On Wed, 2013-08-21 at 13:39 +0300, Eliezer Tamir wrote:
> 
>>
>> Instead of remembering the napi_id for all the sockets in an epoll,
>> we only track the first socket we see with any unique napi_id.
>> The rational for this is that while there may be many thousands of
>> sockets tracked by a single epoll, we expect to only see a handful
>> of unique napi_ids in most cases.
> 
> This looks buggy assumption to me.
> 
> We use epoll() with in the order of millions of fds per epoller, and
> typically one napi_id per cpu.
> 
> With your model, we would have to use nr_cpu epollers and make sure that
> sockets are properly placed on those epollers by their napi_ids.

There is no assumption here on how the user configures epoll.
All we are doing is reducing the list of sockets monitored
by an epoll instance to a smaller subset where each NAPI_ID
appears only once.

The user is free to have an epoll monitor sockets from queues
associated to any CPU.
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