Messages in this thread | | | Date | Wed, 12 Sep 2007 00:10:19 +0100 | From | "Adrian McMenamin" <> | Subject | Re: time_after - what on earth??? |
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On 12/09/2007, Björn Steinbrink <B.Steinbrink@gmx.de> wrote: > On 2007.09.12 00:19:09 +0200, Rene Herman wrote: > > On 09/12/2007 12:15 AM, Adrian McMenamin wrote: > > > >> On 11/09/2007, Rene Herman <rene.herman@gmail.com> wrote: > >>> On 09/12/2007 12:05 AM, Adrian McMenamin wrote: > >>> > >>>> OK, why does this line occasionally return true: > > What exactly is "occassionally"? Does it happen more than once per > boot? If not, and it happens after a certain time after booting, it > might be wrapping of the jiffie counter (see below). > > >>>> > >>>> if ((maple_dev->interval > 0) && (jiffies >maple_dev->when)) > >>>> > >>>> while this one never does (no other changes made): > >>>> > >>>> if ((maple_dev->interval > 0) && (time_after(jiffies, > >>>> maple_dev->when))) > >>> Is maple_dev->when an unsigned long? > >>> > >> Yes. Does that make a difference? > > > > If it had been a signed type, it could've wrapped to something you didn't > > expect, explaining the difference at least... > > > > With an unsigned long, the only diference should be that time_after() deals > > with jiffie wrapping which I assume is not an actual problem here. I'll > > retreat into the shades again... ;-( > > If "occasionally" is limited to once per boot, it might be jiffie > wrapping. IIRC jiffies are initialized so that they wrap after about 5 > minutes of uptime to reveal such bugs without forcing you to wait for > ages just to have the counter wrap for the first time. >
No, I mean "works properly" - ie occasionally evaluates as true - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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