netdev - Re: TSO trimming question

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Message-Id: <20071221143707.fbb0ae60.billfink@mindspring.com>
Date:	Fri, 21 Dec 2007 14:37:07 -0500
From:	Bill Fink <billfink@...dspring.com>
To:	"Ilpo =?ISO-8859-1?Q?J=E4rvinen" ?= <ilpo.jarvinen@...sinki.fi>
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, Ilpo Järvinen wrote:

> 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? :-)

As long as tp->tso_deferred remains u32, pending the other issue.

						-Bill
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