netdev - Re: TSO trimming question

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Message-ID: <Pine.LNX.4.64.0712212056220.31652@kivilampi-30.cs.helsinki.fi>
Date:	Fri, 21 Dec 2007 20:58:35 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Bill Fink <billfink@...dspring.com>
cc:	David Miller <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Netdev <netdev@...r.kernel.org>, John Heffner <jheffner@....edu>
Subject: Re: TSO trimming question

On Fri, 21 Dec 2007, Bill Fink wrote:

> On Fri, 21 Dec 2007, Bill Fink wrote:
> 
> > Or perhaps even:
> > 
> > 	/* Ok, it looks like it is advisable to defer.  */
> > 	tp->tso_deferred = jiffies;
> > 
> > 	/* need to return a non-zero value to defer, which means won't
> > 	 * defer if jiffies == 0 but it's only a 1 in 4 billion event
> > 	 * (and avoids a compare/branch by not checking jiffies)
> > 	 /
> >         return jiffies;
> 
> Ack.  I introduced my own 64-bit to 32-bit issue (too late at night).
> How about:
> 
> 	/* Ok, it looks like it is advisable to defer.  */
> 	tp->tso_deferred = jiffies;
> 
> 	/* this won't defer if jiffies == 0 but it's only a 1 in
> 	 * 4 billion event (and avoids a branch)
> 	 */
> 	return (jiffies != 0);

I'm not sure how the jiffies work but is this racy as well?

Simple return tp->tso_deferred; should work, shouldn't it? :-)


-- 
 i.
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