Date: Sat, 10 Jul 2004 01:18:06 -0400 (EDT) From: Robert Watson <rwatson@freebsd.org> To: "Marc G. Fournier" <scrappy@hub.org> Cc: Steve Kargl <sgk@troutmask.apl.washington.edu> Subject: Re: Native preemption is the culprit [was Re: today's CURRENT lockups] Message-ID: <Pine.NEB.3.96L.1040710011206.19581H-100000@fledge.watson.org> In-Reply-To: <Pine.NEB.3.96L.1040709231313.19581G-100000@fledge.watson.org>
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On Fri, 9 Jul 2004, Robert Watson wrote: > I'm now experiencing extremely hard hangs in the following configurations: > > SMP kernel running SCHED_ULE with hyperthreads > SMP kernel running SCHED_4BSD with hyperthreads > > To generate the load, I'm using the "supersmack" benchark with the > select-key.smack query set with 30 client workers and 10,000 > transactions. I am able to reliable hang the system with one or two > runs. > > By disabling the "#define PREEMPTION" entry in param.h with SCHED_4BSD, > I'm able to complete the benchmark several times in a row without > apparent problems. However, I'll leave it running for a few more hours > and see if I didn't just "get lucky". I'll then try SCHED_ULE w/o > PREEMPTION. > > By "extremely hard" I mean that I am unable to break into the debugger > using a serial break on the serial console. I have not yet been able to > run the test on a system with easily accessible NMI but will attempt to > do so in the next few days. > > I'll give UP a spin with various combinations next. FYI, UP+SCHED_ULE with PREEMPTION hung within three seconds of starting the benchmark. Without PREEMPTION it seems to run fine. So it looks like either PREEMPTION has a problem, or it's triggering an existing problem elsewhere. If it's only one problem, it seems not to depend on either SMP/UP or the scheduler choice. If it's multiple problems, who knows :-). As the MySQL test relies on threading, we could be looking at an edge case involving threading and scheduling/preemption -- the other reports I've seen mention X11/KDE, which would also involve threading. On the other hand, it could just be load. Tomorrow I'll load up a box with non-threaded apps and see what happens. Robert N M Watson FreeBSD Core Team, TrustedBSD Projects robert@fledge.watson.org Principal Research Scientist, McAfee Research
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