netdev - Re: [PATCH 1/2] net: adding memory barrier to the poll and receive callbacks

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Message-ID: <20090629180431.GE2742@ami.dom.local>
Date:	Mon, 29 Jun 2009 20:04:31 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	fbl@...hat.com, nhorman@...hat.com, davem@...hat.com,
	htejun@...il.com, oleg@...hat.com, eric.dumazet@...il.com
Subject: Re: [PATCH 1/2] net: adding memory barrier to the poll and receive
	callbacks

On Mon, Jun 29, 2009 at 10:36:30AM -0700, Davide Libenzi wrote:
> On Mon, 29 Jun 2009, Jarek Poplawski wrote:
> 
> > > I think Oleg already said this, but you can use directly poll_wait() 
> > > without adding another abstraction, and the compiler will drop the double 
> > > check for you:
> > 
> > I think Oleg told about cosmetics and let Jiri to choose. I'd only
> > add it's not mainly about optimization, but easy showing the main
> > difference, of course depending on taste.
> 
> We already have a universally used function to do that, and that's 
> poll_wait().
> That code (adding an extra __poll_wait()) was entirely about 
> optimizations (otherwise why not use the existing poll_wait()?), so if 
> the optimization does not actually take place, IMO it's better to not add 
> an extra API.

OK, you're right, it is about optimization! But IMHO mainly about
reading optimization... I simply guess me and probably Jiri too,
after reading Oleg's variant thought about compiler, instead of the
real difference.

Btw., maybe I miss something but I guess Oleg proposed something in
between: inlining __poll_wait(), which would save us 'extra API' and
compiler doubts. (But I still prefer Jiri's choice. ;-)

Jarek P.
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