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Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at kernel/events/core.c:8485 perf_pmu_register+0x420/0x428

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On Mon, Jun 06, 2016 at 11:29:36AM +0200, Hendrik Brueckner wrote:

> > > Looks like perf_pmu_register does not like to be called twice (once for the counter
> > > and once for the sampling facility).
> > 
> > Twice isn't the problem per se, its trying to register two PMUs for
> > perf_hw_context that is the problem.
> > 
> > The perf core does not expect or deal well with that.
> > 
> > The perf core expects a single HW PMU in that when it schedules
> > hw_context events, and encounters an failure to pmu::add() (because the
> > hw pmu is 'full') it stops trying to add more events.
> 
> On s390, there are actually two distinct measurement facilities and, thus,
> two HW PMUs for each.  There is the hardware counter and hardware sampling
> facility/PMU.

Can you quickly describe the cf one; or provide a link to a document
doing so?

If this is a simple always running counter without interrupt you could
make it a 'software' PMU which can always schedule, similar to the x86
MSR driver (arch/x86/events/msr.c).

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Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at  kernel/events/core.c:8485 perf_pmu_register+0x420/0x428 Peter Zijlstra <peterz@infradead.org> - 2016-06-06 10:30 +0200
  Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at  kernel/events/core.c:8485 perf_pmu_register+0x420/0x428 Hendrik Brueckner <brueckner@linux.vnet.ibm.com> - 2016-06-06 11:30 +0200
  Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at  kernel/events/core.c:8485 perf_pmu_register+0x420/0x428 Peter Zijlstra <peterz@infradead.org> - 2016-06-06 12:30 +0200
    Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at kernel/events/core.c:8485  perf_pmu_register+0x420/0x428 Christian Borntraeger <borntraeger@de.ibm.com> - 2016-06-06 12:50 +0200
    Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at  kernel/events/core.c:8485 perf_pmu_register+0x420/0x428 Hendrik Brueckner <brueckner@linux.vnet.ibm.com> - 2016-06-08 11:10 +0200

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