svn commit: r221703 - in head/sys: amd64/include i386/include
x86/isa x86/x86
Andriy Gapon
avg at FreeBSD.org
Thu May 12 10:44:03 UTC 2011
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 at 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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