Date: Thu, 12 May 2011 13:43:58 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Stanislav Sedov <stas@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org, Jung-uk Kim <jkim@FreeBSD.org> Subject: Re: svn commit: r221703 - in head/sys: amd64/include i386/include x86/isa x86/x86 Message-ID: <4DCBB9EE.8070809@FreeBSD.org> In-Reply-To: <20110512024956.996cd973.stas@FreeBSD.org> References: <201105091734.p49HY0P3006180@svn.freebsd.org> <20110512024956.996cd973.stas@FreeBSD.org>
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on 12/05/2011 12:49 Stanislav Sedov said the following: > On Mon, 9 May 2011 17:34:00 +0000 (UTC) > Jung-uk Kim <jkim@FreeBSD.org> mentioned: > >> Author: jkim >> Date: Mon May 9 17:34:00 2011 >> New Revision: 221703 >> URL: http://svn.freebsd.org/changeset/base/221703 >> >> Log: >> Implement boot-time TSC synchronization test for SMP. This test is executed >> when the user has indicated that the system has synchronized TSCs or it has >> P-state invariant TSCs. For the former case, we may clear the tunable if it >> fails the test to prevent accidental foot-shooting. For the latter case, we >> may set it if it passes the test to notify the user that it may be usable. >> > > Hi, Jung-uk! > > My kernel no longer boots on my Dual Xeon Dell Precision after this > commit. It hangs immediately after the "AP launched" messages. > > I uploaded my verbose boot log from the old kernel to > http://www.SpringDaemons.com/stas/boot.verbose I believe that this was the first stress test for smp_rendezvous() that has uncovered a bug in it. I think that a fix similar to what I committed in my xcpu branch is needed. Theory: - smp_rv_waiters[2] becomes equal to smp_rv_ncpus - [at least] one slave CPU is still in the last call to cpu_spinwait() in smp_rendezvous_action() - master CPU notices that the condition is true, exits smp_rendezvous_cpus() and calls it again - the slave CPU is still in spinwait - the master CPU resets smp_rv_waiters[2] to zero - the slave CPU exits spinwait, see smp_rv_waiters[2] with zero value - endless loop -- Andriy Gapon
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