netdev - Re: [PATCH v6 net-next 2/5] net: implement support for low latency socket polling

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Date:	Wed, 29 May 2013 21:20:35 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Or Gerlitz <or.gerlitz@...il.com>
CC:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>,
	Eric Dumazet <erdnetdev@...il.com>,
	David Miller <davem@...emloft.net>,
	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	<e1000-devel@...ts.sourceforge.net>,
	Willem de Bruijn <willemb@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eilon Greenstien <eilong@...adcom.com>,
	Alex Rosenbaum <alexr@...lanox.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [PATCH v6 net-next 2/5] net: implement support for low latency
 socket polling

On Wed, 2013-05-29 at 17:14 +0300, Or Gerlitz wrote:
> On Wed, May 29, 2013 at 9:39 AM, Eliezer Tamir
> <eliezer.tamir@...ux.intel.com> wrote:
> > Adds a new ndo_ll_poll method and the code that supports and uses it.
> > This method can be used by low latency applications to busy poll Ethernet
> > device queues directly from the socket code. The value of sysctl_net_ll_poll
> > controls how many microseconds to poll. Set to zero to disable.
> 
> Unlike with TCP sockets, UDP sockets may receive packets from multiple
> sources and hence the receiving context may be steered to be executed
> on different cores through RSS or other Flow-Steering HW mechanisms
> which could mean different napi contexts for the same socket, is that
> a problem here? what's the severity?

Maybe ARFS could be extended so the driver can tell whether a UDP socket
it's steering for is connected or not.  Then for disconnected sockets
the driver can use a filter that only matches destination address.
(Though that's probably undesirable if the socket has SO_REUSEPORT set.)

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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