From: Con Kolivas <kernel@kolivas.org>
To: mru@users.sourceforge.net (=?iso-8859-1?q?M=E5ns?=
	=?iso-8859-1?q?=20Rullg=E5rd?=),
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH]O18.1int
Date: Mon, 25 Aug 2003 23:32:25 +1000
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On Mon, 25 Aug 2003 22:49, M?ns Rullg?rd wrote:
> Con Kolivas <kernel@kolivas.org> writes:
> >> >> >> Vanilla test1 has the spin effect.  Test2 doesn't.  I haven't
> >> >> >> tried vanilla test3 or test4.  As I've said, the O16.2-O16.3 patch
> >> >> >> introduced the problem.  With that patch reversed, everything is
> >> >> >> fine.  What problem does that patch fix?
> >> >> >
> >> >> > It's a generic fix for priority inversion but it induces badness in
> >> >> > smp, and latency in task preemption on up so it's not suitable.
> >> >>
> >> >> Now I'm confused.  If that patch is bad, then why is it in O18?
> >> >
> >> > No, the 16.2 patch is bad. 16.3 backed it out.
> >>
> >> OK, but it somehow made XEmacs behave badly.
> >
> > Well it was a generic fix in 16.2 that helped XEmacs as I said. O15
> > also had a generic fix (child not preempting it's parent) but that
> > too was covering up the real issue, but it wasnt as drastic as 16.2.
>
> Of the kernels I've tested, only test1 vanilla and O16.3 and later
> show the problem.  Btw, is it related to the XEmacs regexp search
> problem, or is that a different one?

Same thing. Both examples of priority inversion. In your case a parent child 
interaction which was worked around in O15. That interaction seems the more 
common case.

Con

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