Messages in this thread | | | Date | Wed, 12 Sep 2007 01:09:40 +0200 | From | Björn Steinbrink <> | Subject | Re: time_after - what on earth??? |
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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.
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