linux-kernel - Re: [2.6.28-rc1 regression] wmifinfo dockapp takes 100% of cpu (bisected)

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Message-Id: <20081030000442.fdc831c1.akpm@linux-foundation.org>
Date:	Thu, 30 Oct 2008 00:04:42 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Ray Lee" <ray-lk@...rabbit.org>
Cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"Marcin Slusarz" <marcin.slusarz@...il.com>,
	"Carlos R. Mafra" <crmafra2@...il.com>,
	"Arjan van de Ven" <arjan@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6.28-rc1 regression] wmifinfo dockapp takes 100% of cpu
 (bisected)

On Sat, 25 Oct 2008 12:38:22 -0700 "Ray Lee" <ray-lk@...rabbit.org> wrote:

> On Sat, Oct 25, 2008 at 12:12 PM, Arjan van de Ven <arjan@...radead.org> wrote:
> > On Sat, 25 Oct 2008 20:03:27 +0200
> > Marcin Slusarz <marcin.slusarz@...il.com> wrote:
> >> > >           if (copy_from_user(&tv, tvp, sizeof(tv)))
> >> > >                   return -EFAULT;
> >> > >
> >> > > +         while (tv.tv_usec > USEC_PER_SEC && i < 1000) {
> >>                                   ^
> >> should be >=
> >
> > yeah thanks for catching that. Note to self: don't code before coffee
> >
> > I'm not very happy with a while loop; but at least it solves the problem
> >
> > I'll try to make it nicer than this ...
> 
> Regardless, you may wish to make a set_normalized_timeval and place it
> in kernel/time.c right after the current set_nromalized_timespec.

Yes, this comes up fairly regularly and we would benefit from having a
normalize-a-timeval library function.

I don't think it should be implemented via a while loop though.  That's
acceptable with timespecs, which can only loop four or so times.  But
timevals use microseconds and can loop thousands of times and hence a
normalization function should use division.

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