linux-kernel - Re: [PATCH v3 07/10] perf: Cleanup for HAVE_SYNC_COMPARE_AND_SWAP

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Date:   Sat, 10 Jul 2021 15:36:53 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Leo Yan <leo.yan@...aro.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 07/10] perf: Cleanup for
 HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT

On 4/07/21 10:16 am, Leo Yan wrote:
> Since the __sync functions have been dropped, This patch removes unused
> build and checking for HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT in perf tool.
> 
> Note, there have a test for SYNC_COMPARE_AND_SWAP and the test file is
> located in build/feature/test-sync-compare-and-swap.c.  Since there
> still has several components using the sync functions, it's deliberately
> to not be removed.

I don't quite follow that.  If they aren't using the feature test
macro, then why keep the feature test?

> 
>   $ cd linux/tools
>   $ git grep __sync_val_compare_and_swap | awk '{ printf $1"\n" }'
>   build/feature/test-sync-compare-and-swap.c:
>   include/asm-generic/atomic-gcc.h:
>   testing/selftests/bpf/progs/atomics.c:
>   testing/selftests/bpf/progs/atomics.c:
>   testing/selftests/bpf/progs/atomics.c:
>   testing/selftests/bpf/progs/atomics.c:
>   testing/selftests/futex/include/atomic.h:
>   testing/selftests/futex/include/futextest.h:
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/Makefile.config | 4 ----
>  tools/perf/util/auxtrace.c | 5 -----
>  2 files changed, 9 deletions(-)
> 
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index eb8e487ef90b..4a0d9a6defc7 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -349,10 +349,6 @@ CXXFLAGS += $(INC_FLAGS)
>  
>  LIBPERF_CFLAGS := $(CORE_CFLAGS) $(EXTRA_CFLAGS)
>  
> -ifeq ($(feature-sync-compare-and-swap), 1)
> -  CFLAGS += -DHAVE_SYNC_COMPARE_AND_SWAP_SUPPORT
> -endif
> -
>  ifeq ($(feature-pthread-attr-setaffinity-np), 1)
>    CFLAGS += -DHAVE_PTHREAD_ATTR_SETAFFINITY_NP
>  endif
> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> index 44bd04dbb6d6..db6255b55c90 100644
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c
> @@ -130,11 +130,6 @@ int auxtrace_mmap__mmap(struct auxtrace_mmap *mm,
>  		return 0;
>  	}
>  
> -#if BITS_PER_LONG != 64 && !defined(HAVE_SYNC_COMPARE_AND_SWAP_SUPPORT)
> -	pr_err("Cannot use AUX area tracing mmaps\n");
> -	return -1;
> -#endif
> -
>  	pc->aux_offset = mp->offset;
>  	pc->aux_size = mp->len;
>  
>