Date: Thu, 12 May 2011 07:40:45 -0400 From: John Baldwin <jhb@FreeBSD.org> To: Andriy Gapon <avg@FreeBSD.org> Cc: src-committers@FreeBSD.org, neel@FreeBSD.org, svn-src-all@FreeBSD.org, Stanislav Sedov <stas@FreeBSD.org>, svn-src-head@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: <4DCBC73D.9070006@FreeBSD.org> In-Reply-To: <4DCBBEF5.4090004@FreeBSD.org> References: <201105091734.p49HY0P3006180@svn.freebsd.org> <20110512024956.996cd973.stas@FreeBSD.org> <4DCBB9EE.8070809@FreeBSD.org> <20110512035522.e42b379c.stas@FreeBSD.org> <4DCBBCBE.5020004@FreeBSD.org> <4DCBBEF5.4090004@FreeBSD.org>
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On 5/12/11 7:05 AM, Andriy Gapon wrote: > on 12/05/2011 13:55 John Baldwin said the following: >> On 5/12/11 6:55 AM, Stanislav Sedov wrote: >>> On Thu, 12 May 2011 13:43:58 +0300 >>> Andriy Gapon<avg@FreeBSD.org> mentioned: >>> >>>> >>>> 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 >>>> >>> >>> That might explain it. >>> Do you have a patch for me to try? >>> >>> Thanks! >>> >> >> The NetApp folks working on BHyVe also ran into this. They have a fix that I >> think sounds reasonable which is to add a generation count to the smp rendezvous >> "structure" and have waiting CPUs stop waiting if the generation count changes. >> > > This is an adaption of my patch in xcpu branch to head (not tested): Hmmm, this might be interesting. I think you want to always wait for this though even if you have a teardown function. -- John Baldwin
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