On 08/31/2010 10:54 PM, Michael Ellerman wrote: > On Tue, 2010-08-31 at 00:12 -0700, Darren Hart wrote: > .. >> >> When running with the function plugin I had to stop the trace >> immediately before entering start_secondary after an online or my traces >> would not include the pseries_mach_cpu_die function, nor the tracing I >> added there (possibly buffer size, I am using 2048). The following trace >> was collected using "trace-cmd record -p function -e irq -e sched" and >> has been filtered to only show CPU [001] (the CPU undergoing the >> offline/online test, and the one seeing preempt_count (pcnt) go to >> ffffffff after cede. The function tracer does not indicate anything >> running on the CPU other than the HCALL - unless the __trace_hcall* >> commands might be to blame. > > It's not impossible. Though normally they're disabled right, so the only > reason they're running is because you're tracing. So if they are causing > the bug then that doesn't explain why you see it normally. > > Still, might be worth disabling just the hcall tracepoints just to be > 100% sure.
A couple of updates. I was working from tip/rt/head, which has been stale for some months now. I switched to tip/rt/2.6.33 and the preempt_count() change over cede went away. I now see the live hang that Will has reported. Before I dive into the live hang, I want to understand what fixed the preempt_count() change. That might start pointing us in the right direction for the live hang. I did an inverted git bisect between tip/rt/head and tip/rt/2.6.33 to try and locate the fix. I've narrowed it down to the 2.6.33.6 merge: # git show 7e1af1172bbd4109d09ac515c5d376f633da7cff commit 7e1af1172bbd4109d09ac515c5d376f633da7cff Merge: d8e94db 9666790 Author: Thomas Gleixner <[email protected]> Date: Tue Jul 13 16:01:16 2010 +0200 Merge git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-2.6.33.y Conflicts: Makefile Signed-off-by: Thomas Gleixner <[email protected]> Visual inspection yields two patches of interest: f8b67691828321f5c85bb853283aa101ae673130 powerpc/pseries: Make query-cpu-stopped callable outside hotplug cpu aef40e87d866355ffd279ab21021de733242d0d5 powerpc/pseries: Only call start-cpu when a CPU is stopped I'm going to try reverting these today and see if they addressed the issue indirectly. -- Darren Hart IBM Linux Technology Center Real-Time Linux Team _______________________________________________ Linuxppc-dev mailing list [email protected] https://lists.ozlabs.org/listinfo/linuxppc-dev
