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From:   Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>
Date:   Fri, 11 Oct 2019 11:38:03 -0300
To:     Leo Yan <leo.yan@linaro.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/2] perf test: Avoid infinite loop for task exit case
Message-ID: <20191011143803.GB32176@kernel.org>
References: <20191011091942.29841-1-leo.yan@linaro.org>
 <20191011091942.29841-2-leo.yan@linaro.org>
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Em Fri, Oct 11, 2019 at 05:19:42PM +0800, Leo Yan escreveu:
> When execute task exit testing case, Perf tool stucks in this case and
> doesn't return back on Arm64 Juno board.
> 
> After dig into this issue, since Juno board has Arm's big.LITTLE CPUs,
> thus the PMUs are not compatible between the big CPUs and little CPUs.
> This leads to PMU event cannot be enabled properly when the traced task
> is migrated from one variant's CPU to another variant.  Finally, the
> test case runs into infinite loop for cannot read out any event data
> after return from polling.

Thanks, I'll go over this after I finish the current pull request,

- Arnaldo
 
> Eventually, we need to work out formal solution to allow PMU events can
> be freely migrated from one CPU variant to another, but this is a
> difficult task and a different topic.  This patch tries to fix the Perf
> test case to avoid infinite loop, when the testing detects 1000 times
> retrying for reading empty events, it will directly bail out and return
> failure.  This allows the Perf tool can continue its other test cases.
> 
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
>  tools/perf/tests/task-exit.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/tools/perf/tests/task-exit.c b/tools/perf/tests/task-exit.c
> index ca0a6ca43b13..d85c9f608564 100644
> --- a/tools/perf/tests/task-exit.c
> +++ b/tools/perf/tests/task-exit.c
> @@ -53,6 +53,7 @@ int test__task_exit(struct test *test __maybe_unused, int subtest __maybe_unused
>  	struct perf_cpu_map *cpus;
>  	struct perf_thread_map *threads;
>  	struct mmap *md;
> +	int retry_count = 0;
>  
>  	signal(SIGCHLD, sig_handler);
>  
> @@ -132,6 +133,13 @@ int test__task_exit(struct test *test __maybe_unused, int subtest __maybe_unused
>  out_init:
>  	if (!exited || !nr_exit) {
>  		evlist__poll(evlist, -1);
> +
> +		if (retry_count++ > 1000) {
> +			pr_debug("Failed after retrying 1000 times\n");
> +			err = -1;
> +			goto out_free_maps;
> +		}
> +
>  		goto retry;
>  	}
>  
> -- 
> 2.17.1

-- 

- Arnaldo