Date: Sat, 23 Mar 2013 12:32:55 -0600 From: Ian Lepore <ian@FreeBSD.org> To: MagnusNilsson <magnus.nilsson@gmail.com> Cc: freebsd-arm@FreeBSD.org Subject: Re: Preemption on MV78100 (ARMv5TE)? Message-ID: <1364063575.1157.155.camel@revolution.hippie.lan> In-Reply-To: <1364062508310-5798411.post@n5.nabble.com> References: <1364062508310-5798411.post@n5.nabble.com>
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On Sat, 2013-03-23 at 11:15 -0700, MagnusNilsson wrote: > I am looking for information about FreeBSD 8.2 on Marvell MV78100 (Discovery > SOC) - an ARMv5TE - with preemption enabled. > My kernel is stable, but if I enable preemption it promptly crashes - during > or within minutes of boot. > > My configuration is similar to: > http://svn.freebsd.org/base/head/sys/arm/conf/DB-78XXX > I notice that this configuration does not have the PREEMPTION option - not > even commented - whereas many other configurations in: > http://svn.freebsd.org/base/head/sys/arm/conf/ > do have it. > > I am interested to hear if anyone has been able to run MV78100 (or similar) > with preemption enabled - and in that case what your configuration and > FreeBSD version is - or if anyone can confirm that preemption is not > implemented for this processor. > > Thank you. Can you provide any information about the crashes? In my experience with 8.2 on arm (extensive, we use it at work, but with a variety of fixes pulled in from 9 and 10), the main source of problems has been busdma cache coherency problems. A variety of such problems have been fixed since 8.2, but I'm not sure all the fixes have been merged back to the 8-stable branch. I've never tried enabling PREEMPTION, I'll give that a try. I'm not sure why you're enabling it, but something to try that may give you most of the same benefits would be to compile with HZ=1000 or even higher, to shorten the scheduling quantum. Most of our ARM configs have HZ=100, but I've successfully run with HZ=4000 even on a low-end at91 chip running at 180mhz (just to see if I could, we don't normally do that on our products at work). -- Ian
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