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

From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	"linux-kernel@vger.kernel.org >> Linux Kernel Mailing List" 
	<linux-kernel@vger.kernel.org>
Subject: Re: 4.7-rc1/s390: WARNING: CPU: 5 PID: 1 at kernel/events/core.c:8485 perf_pmu_register+0x420/0x428
Date: Mon, 6 Jun 2016 12:44:50 +0200	[thread overview]
Message-ID: <201606061045.u56AhkFw009429@mx0a-001b2d01.pphosted.com> (raw)
In-Reply-To: <20160606102900.GC30909@twins.programming.kicks-ass.net>

On 06/06/2016 12:29 PM, Peter Zijlstra wrote:
> 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?

http://www-01.ibm.com/support/docview.wss?uid=isg26fcd1cc32246f4c8852574ce0044734a

(or google for "The Load-Program-Parameter and the CPU-Measurement Facilities"
or SA23-2260)

> 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).

Its a bunch of counters for events like cache writes, cycles, instructions,
but Hendrik can probably better answer that specific question.