netdev - Re: [RFC PATCH 1/5] net: implement support for low latency socket polling

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Message-ID: <1362413759.15793.98.camel@edumazet-glaptop>
Date:	Mon, 04 Mar 2013 08:15:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eliezer Tamir <eliezer.tamir@...ux.intel.com>
Cc:	Eliezer Tamir <eliezer.tamir@...ux.jf.intel.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	Dave Miller <davem@...emloft.net>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Willem de Bruijn <willemb@...gle.com>,
	Andi Kleen <andi@...stfloor.org>, HPA <hpa@...or.com>,
	Eliezer Tamir <eliezer@...ir.org.il>
Subject: Re: [RFC PATCH 1/5] net: implement support for low latency socket
 polling

On Mon, 2013-03-04 at 17:28 +0200, Eliezer Tamir wrote:
> On 04/03/2013 16:52, Eric Dumazet wrote:
> > On Mon, 2013-03-04 at 10:43 +0200, Eliezer Tamir wrote:
> >
> >> One could for example increment the generation id every time the RTNL is
> >> taken. or is this too much?
> >
> > RTNL is taken for a lot of operations, it would be better to have a
> > finer grained increment.
> 
> If is taken rarely enough it will still be worth it.
> 

Yes, but eventually it makes attempts to get rid of RTNL a nightmare.

When adding new network features, just use the right semantic from the
beginning.

> Otherwise it may be hard to know what operations need to invalidate the 
> napi reference. It can very well be HW dependent, and then you end up 
> adding a function for drivers to call to do the invalidation.
> 
> Or we can decide that we only care about catastrophic events and only 
> worry about a napi completely going away and not worry about 
> configuration changes.(Polling the wrong queue will not kill you, it's 
> just a waste of perfectly good CPU cycles.)

As long as the incoming packets are able to update the information, who
cares if one packet missed the poll ?
 


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