linux-kernel - Re: [PATCH v4 07/11] perf auxtrace: Remove auxtrace_mmap__read_snapshot

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Date:   Mon, 12 Jul 2021 17:32:11 +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 v4 07/11] perf auxtrace: Remove
 auxtrace_mmap__read_snapshot_head()

On 11/07/21 1:41 pm, Leo Yan wrote:
> Since the function auxtrace_mmap__read_snapshot_head() is exactly same
> with auxtrace_mmap__read_head(), whether the session is in snapshot mode
> or not, it's unified to use function auxtrace_mmap__read_head() for
> reading AUX buffer head.
> 
> And the function auxtrace_mmap__read_snapshot_head() is unused so this
> patch removes it.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  tools/perf/util/auxtrace.c |  5 ++---
>  tools/perf/util/auxtrace.h | 10 ----------
>  2 files changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> index cb19669d2a5b..7958e17229ea 100644
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c
> @@ -1686,13 +1686,12 @@ static int __auxtrace_mmap__read(struct mmap *map,
>  	union perf_event ev;
>  	void *data1, *data2;
>  
> +	head = auxtrace_mmap__read_head(mm);
> +
>  	if (snapshot) {
> -		head = auxtrace_mmap__read_snapshot_head(mm);
>  		if (auxtrace_record__find_snapshot(itr, mm->idx, mm, data,
>  						   &head, &old))

That leaves a nested 'if' which is not kernel style i.e. could be

	if (snapshot &&
	    auxtrace_record__find_snapshot(itr, mm->idx, mm, data, &head, &old))


>  			return -1;
> -	} else {
> -		head = auxtrace_mmap__read_head(mm);
>  	}
>  
>  	if (old == head)
> diff --git a/tools/perf/util/auxtrace.h b/tools/perf/util/auxtrace.h
> index 4f9176368134..d68a5e80b217 100644
> --- a/tools/perf/util/auxtrace.h
> +++ b/tools/perf/util/auxtrace.h
> @@ -440,16 +440,6 @@ struct auxtrace_cache;
>  
>  #ifdef HAVE_AUXTRACE_SUPPORT
>  
> -static inline u64 auxtrace_mmap__read_snapshot_head(struct auxtrace_mmap *mm)
> -{
> -	struct perf_event_mmap_page *pc = mm->userpg;
> -	u64 head = READ_ONCE(pc->aux_head);
> -
> -	/* Ensure all reads are done after we read the head */
> -	smp_rmb();
> -	return head;
> -}
> -
>  static inline u64 auxtrace_mmap__read_head(struct auxtrace_mmap *mm)
>  {
>  	struct perf_event_mmap_page *pc = mm->userpg;
>