Messages in this thread | | | Date | Wed, 12 Sep 2007 01:16:22 +0200 | From | Rene Herman <> | Subject | Re: time_after - what on earth??? |
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On 09/12/2007 01:09 AM, Björn Steinbrink 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.
Yes, but if jiifie wrapping was the problem, I'd expect the contrary behaviour with the time_after() one hitting while the > one does not.
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