Re: [PATCH v2 4/4] perf/x86/uncore: modularize Intel uncore driver

[Stephane Eranian]

On Tue, Apr 22, 2014 at 1:35 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> * Yan, Zheng <zheng.z.yan@xxxxxxxxx> wrote:
>
>> On 04/18/2014 06:53 PM, Ingo Molnar wrote:
>> >
>> > * Yan, Zheng <zheng.z.yan@xxxxxxxxx> wrote:
>> >
>> >> This patch adds support for building Intel uncore driver as module.
>> >> It adds clean-up code and config option for the Intel uncore driver
>> >>
>> >> Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
>> >> ---
>> >> Changes since v1:
>> >>  move config option to "General setup/Kernel Performance Events and Counters"
>> >>
>> >>  arch/x86/kernel/cpu/Makefile                  |  3 +-
>> >>  arch/x86/kernel/cpu/perf_event_intel_uncore.c | 48 ++++++++++++++++++++++++---
>> >>  init/Kconfig                                  | 10 ++++++
>> >>  3 files changed, 56 insertions(+), 5 deletions(-)
>> >>
>> >> diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
>> >> index 7fd54f0..5d3da70 100644
>> >> --- a/arch/x86/kernel/cpu/Makefile
>> >> +++ b/arch/x86/kernel/cpu/Makefile
>> >> @@ -36,7 +36,8 @@ obj-$(CONFIG_CPU_SUP_AMD)                += perf_event_amd_iommu.o
>> >>  endif
>> >>  obj-$(CONFIG_CPU_SUP_INTEL)               += perf_event_p6.o perf_event_knc.o perf_event_p4.o
>> >>  obj-$(CONFIG_CPU_SUP_INTEL)               += perf_event_intel_lbr.o perf_event_intel_ds.o perf_event_intel.o
>> >> -obj-$(CONFIG_CPU_SUP_INTEL)               += perf_event_intel_uncore.o perf_event_intel_rapl.o
>> >> +obj-$(CONFIG_CPU_SUP_INTEL)               += perf_event_intel_rapl.o
>> >> +obj-$(CONFIG_PERF_X86_INTEL_UNCORE)       += perf_event_intel_uncore.o
>> >>  endif
>> >>
>> >>
>> >> diff --git a/arch/x86/kernel/cpu/perf_event_intel_uncore.c b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
>> >> index 618d502..fd5e883 100644
>> >> --- a/arch/x86/kernel/cpu/perf_event_intel_uncore.c
>> >> +++ b/arch/x86/kernel/cpu/perf_event_intel_uncore.c
>> >
>> > So I'm not willing to apply this patch until the documentation of
>> > perf_event_intel_uncore.c is improved. Right now the file starts
>> > without a single comment (!). Just lines after lines of code, without
>> > any explanation what it does, what its scope is, etc.
>>
>> there are comments mark the scope of code for different CPU.
>>
>> >
>> > How should even a knowledgable user know about what it's all about?
>> >
>> > That problem percolates to the Kconfig entry as well:
>> >
>>
>> Most of the codes without comments are hardware specific codes. The
>> corresponding contents in Intel uncore documents are big
>> tables/lists, nothing tricky/interesting. I really don't know how to
>> comment these code.
>
> Have a look at other PMU drivers, such as
> arch/x86/kernel/cpu/perf_event_intel_rapl.c, which begin with a
> general explanation attached below.
>
I think a more useful modularization would be to split that huge file
(perf_event_intel_uncore.c) into smaller files like we do for the core
PMU. There is just too much stuff in this file for my own taste. Hard
to navigate and I spend quite some time looking at it and modifying it!

You could follow the model of the core PMU support files.
You'd have a "core" file with the common routines, and then
a file perf processor:
    - perf_event_intel_uncore.c
    - perf_event_intel_snbep_uncore.c
    - perf_event_intel_nhmex_uncore.c
    - perf_event_intel_ivt_uncore.c
    - ...

Each processor specific module, would be a kernel module.
The core could be one too. Note that this would not alleviate
the need for some basic descriptions at the beginning of
each file outlining the PMU boxes exported to a minimum.


> /*
>  * perf_event_intel_rapl.c: support Intel RAPL energy consumption counters
>  * Copyright (C) 2013 Google, Inc., Stephane Eranian
>  *
>  * Intel RAPL interface is specified in the IA-32 Manual Vol3b
>  * section 14.7.1 (September 2013)
>  *
>  * RAPL provides more controls than just reporting energy consumption
>  * however here we only expose the 3 energy consumption free running
>  * counters (pp0, pkg, dram).
>  *
>  * Each of those counters increments in a power unit defined by the
>  * RAPL_POWER_UNIT MSR. On SandyBridge, this unit is 1/(2^16) Joules
>  * but it can vary.
>  *
>  * Counter to rapl events mappings:
>  *
>  *  pp0 counter: consumption of all physical cores (power plane 0)
>  *        event: rapl_energy_cores
>  *    perf code: 0x1
>  *
>  *  pkg counter: consumption of the whole processor package
>  *        event: rapl_energy_pkg
>  *    perf code: 0x2
>  *
>  * dram counter: consumption of the dram domain (servers only)
>  *        event: rapl_energy_dram
>  *    perf code: 0x3
>  *
>  * dram counter: consumption of the builtin-gpu domain (client only)
>  *        event: rapl_energy_gpu
>  *    perf code: 0x4
>  *
>  * We manage those counters as free running (read-only). They may be
>  * use simultaneously by other tools, such as turbostat.
>  *
>  * The events only support system-wide mode counting. There is no
>  * sampling support because it does not make sense and is not
>  * supported by the RAPL hardware.
>  *
>  * Because we want to avoid floating-point operations in the kernel,
>  * the events are all reported in fixed point arithmetic (32.32).
>  * Tools must adjust the counts to convert them to Watts using
>  * the duration of the measurement. Tools may use a function such as
>  * ldexp(raw_count, -32);
>  */
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