linux-kernel - Re: [PATCH v8 1/3] perf: cavium: Support memory controller PMU counters

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Date:   Wed, 26 Jul 2017 15:10:58 +0200
From:   Jan Glauber <jan.glauber@...iumnetworks.com>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Will Deacon <will.deacon@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/3] perf: cavium: Support memory controller PMU
 counters

On Wed, Jul 26, 2017 at 01:47:35PM +0100, Suzuki K Poulose wrote:
> On 26/07/17 12:19, Jan Glauber wrote:
> >On Tue, Jul 25, 2017 at 04:39:18PM +0100, Suzuki K Poulose wrote:
> >>On 25/07/17 16:04, Jan Glauber wrote:
> >>>Add support for the PMU counters on Cavium SOC memory controllers.
> >>>
> >>>This patch also adds generic functions to allow supporting more
> >>>devices with PMU counters.
> >>>
> >>>Properties of the LMC PMU counters:
> >>>- not stoppable
> >>>- fixed purpose
> >>>- read-only
> >>>- one PCI device per memory controller
> >>>
> >>>Signed-off-by: Jan Glauber <jglauber@...ium.com>
> >>>---
> >>>drivers/perf/Kconfig       |   8 +
> >>>drivers/perf/Makefile      |   1 +
> >>>drivers/perf/cavium_pmu.c  | 424 +++++++++++++++++++++++++++++++++++++++++++++
> >>>include/linux/cpuhotplug.h |   1 +
> >>>4 files changed, 434 insertions(+)
> >>>create mode 100644 drivers/perf/cavium_pmu.c
> >>>
> >>>diff --git a/drivers/perf/Kconfig b/drivers/perf/Kconfig
> >>>index e5197ff..a46c3f0 100644
> >>>--- a/drivers/perf/Kconfig
> >>>+++ b/drivers/perf/Kconfig
> >>>@@ -43,4 +43,12 @@ config XGENE_PMU
> >>>        help
> >>>          Say y if you want to use APM X-Gene SoC performance monitors.
> >>>
> >>>+config CAVIUM_PMU
> >>>+	bool "Cavium SOC PMU"
> >>
> >>Is there any specific reason why this can't be built as a module ?
> >
> >Yes. I don't know how to load the module automatically. I can't make it
> >a pci driver as the EDAC driver "owns" the device (and having two
> >drivers for one device wont work as far as I know). I tried to hook
> >into the EDAC driver but the EDAC maintainer was not overly welcoming
> >that approach.
> 
> >
> >And while it would be possible to have it a s a module I think it is of
> >no use if it requires manualy loading. But maybe there is a simple
> >solution I'm missing here?
> 
> 
> If you are talking about a Cavium specific EDAC driver, may be we could
> make that depend on this driver "at runtime" via symbols (may be even,
> trigger the probe of PMU), which will be referenced only when CONFIG_CAVIUM_PMU
> is defined. It is not the perfect solution, but that should do the trick.

I think that is roughly what I proposed in v6. Can you have a look at:

https://lkml.org/lkml/2017/6/23/333
https://patchwork.kernel.org/patch/9806427/

Probably there is a better way to do it. Or maybe we just keep it as
built-in for the time being.

--Jan