From owner-freebsd-hackers@FreeBSD.ORG  Thu May 31 14:44:56 2012
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Date: Thu, 31 May 2012 16:37:31 +0200
From: Fabian Keil <freebsd-listen@fabiankeil.de>
To: Ryan Stone <rysto32@gmail.com>
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Cc: freebsd-hackers@freebsd.org, Chadd <adrian@freebsd.org>,
	Alexander Motin <mav@freebsd.org>, Andriy Gapon <avg@freebsd.org>, Adrian
Subject: Re: ULE/sched issues on stable/9 - why isn't preemption occuring?
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Ryan Stone <rysto32@gmail.com> wrote:

> On Thu, May 31, 2012 at 8:33 AM, Andriy Gapon <avg@freebsd.org> wrote:
> > In this vein it might make sense to enable KTR and KTR_SCHED in GENERIC.
>=20
> KTR_SCHED comes with a performance hit.  Besides, with the DTrace
> sched provider that I committed this month (and MFC'ed yesterday) you
> can collect schedgraph data with a D script.

Unfortunately DTrace's timestamp itself doesn't always
work reliably on FreeBSD, and schedgraph.d depends on it.

On my system DTrace's timestamp seems to work with
kern.timecounter.hardware=3DHPET and dev.cpu.0.cx_lowest=3DC2
(or C1) but seems to tick much too slow with dev.cpu.0.cx_lowest=3DC3:
http://lists.freebsd.org/pipermail/freebsd-current/2011-August/026710.html

Fabian

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