linux-kernel - Re: [PATCH v2 1/5] perf: arm64: Add test to check userspace access to hardware counters.

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Date:   Fri, 5 Jul 2019 11:54:36 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Raphael Gault <raphael.gault@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        mingo@...hat.com, peterz@...radead.org, catalin.marinas@....com,
        will.deacon@....com, mark.rutland@....com
Subject: Re: [PATCH v2 1/5] perf: arm64: Add test to check userspace access
 to hardware counters.

Em Fri, Jul 05, 2019 at 09:55:37AM +0100, Raphael Gault escreveu:
> This test relies on the fact that the PMU registers are accessible
> from userspace. It then uses the perf_event_mmap_page to retrieve
> the counter index and access the underlying register.
> 
> This test uses sched_setaffinity(2) in order to run on all CPU and thus
> check the behaviour of the PMU of all cpus in a big.LITTLE environment.
> 
> Signed-off-by: Raphael Gault <raphael.gault@....com>
> ---
>  tools/perf/arch/arm64/include/arch-tests.h |   6 +
>  tools/perf/arch/arm64/tests/Build          |   1 +
>  tools/perf/arch/arm64/tests/arch-tests.c   |   4 +
>  tools/perf/arch/arm64/tests/user-events.c  | 255 +++++++++++++++++++++
>  4 files changed, 266 insertions(+)
>  create mode 100644 tools/perf/arch/arm64/tests/user-events.c
> 
> diff --git a/tools/perf/arch/arm64/include/arch-tests.h b/tools/perf/arch/arm64/include/arch-tests.h
> index 90ec4c8cb880..a9b17ae0560b 100644
> --- a/tools/perf/arch/arm64/include/arch-tests.h
> +++ b/tools/perf/arch/arm64/include/arch-tests.h
> @@ -2,11 +2,17 @@
>  #ifndef ARCH_TESTS_H
>  #define ARCH_TESTS_H
>  
> +#define __maybe_unused	__attribute__((unused))


What is wrong with using:

#include <linux/compiler.h>

?

[acme@...co perf]$ find tools/perf/ -name "*.[ch]" | xargs grep __maybe_unused | wc -l
1115
[acme@...co perf]$ grep __maybe_unused tools/include/linux/compiler.h
#ifndef __maybe_unused
# define __maybe_unused		__attribute__((unused))
[acme@...co perf]$

Also please don't break strings in multiple lines just to comply with
the 80 column limit. That is ok when you have multiple lines ending with
a newline, but otherwise just makes it look ugly.

- Arnaldo