linux-kernel - Re: [PATCH] perf bench: fix assert when NDEBUG is defined

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Date:	Mon, 3 Sep 2012 08:21:08 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Irina Tirdea <irina.tirdea@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] perf bench: fix assert when NDEBUG is defined

On Mon, Sep 3, 2012 at 4:45 AM, Namhyung Kim <namhyung@...nel.org> wrote:
> On Mon, 3 Sep 2012 03:04:32 +0300, Irina Tirdea wrote:
>> From: Irina Tirdea <irina.tirdea@...el.com>
>>
>> When NDEBUG is defined, the assert macro will be expanded to nothing.
>> Some assert calls used in perf are also including some functionality
>> (e.g. system calls), not only validity checks. Therefore, if NDEBUG is
>> defined, these functionality will be removed along with the assert.
>>
>> The functionality of the program needs to be separated from the assert checks.
>> In perf, BUG_ON is also defined on assert, so we need to fix these statements
>> too.
>>
>> Signed-off-by: Irina Tirdea <irina.tirdea@...el.com>
>> ---
>>  tools/perf/bench/mem-memcpy.c |    8 +++++---
>>  tools/perf/bench/mem-memset.c |    8 +++++---
>>  tools/perf/bench/sched-pipe.c |    6 ++++--
>>  3 files changed, 14 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/perf/bench/mem-memcpy.c b/tools/perf/bench/mem-memcpy.c
>> index 02dad5d..bccb783 100644
>> --- a/tools/perf/bench/mem-memcpy.c
>> +++ b/tools/perf/bench/mem-memcpy.c
>> @@ -144,17 +144,19 @@ static double do_memcpy_gettimeofday(memcpy_t
>> fn, size_t len, bool prefault)
>>  {
>>       struct timeval tv_start, tv_end, tv_diff;
>>       void *src = NULL, *dst = NULL;
>> -     int i;
>> +     int i, ret;
>>
>>       alloc_mem(&src, &dst, len);
>>
>>       if (prefault)
>>               fn(dst, src, len);
>>
>> -     BUG_ON(gettimeofday(&tv_start, NULL));
>> +     ret = gettimeofday(&tv_start, NULL);
>> +     BUG_ON(ret);
>
> I think one of good thing of assert is that it outputs the exact failure
> condition when it fails.  So with patch, it will convert
>
>   Assertion `gettimeofday(&tv_start, NULL)' failed.
>
> into
>
>   Assertion `ret' failed.
>
> which is not so informative.
>
> So I'd rather suggest using more descriptive names like ret_gtod ?

No, please don't do that. That'll make the code ugly and it's really
just papering over the fact that the assertions should be converted to
proper error handling.
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