Re: [PATCH v5 10/11] trace: add trace_performance facility to debug performance issues

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 17, 2014, 17:11 UTC
Message-ID: <xmqqsin3mpfe.fsf@gitster.dls.corp.google.com>
In-Reply-To: <53980CD8.5090801@gmail.com>

Karsten Blees <karsten.blees@gmail.com> writes:

Show 25 quoted lines

> Simple use case (measure one code section):
>
>   uint64_t start = getnanotime();
>   /* code section to measure */
>   trace_performance_since(start, "foobar");
>
> Medium use case (measure consecutive code sections):
>
>   uint64_t start = getnanotime();
>   /* first code section to measure */
>   start = trace_performance_since(start, "first foobar");
>   /* second code section to measure */
>   trace_performance_since(start, "second foobar");
>
> Complex use case (measure repetitive code sections):
>
>   uint64_t t = 0;
>   for (;;) {
>     /* ignore */
>     t -= getnanotime();
>     /* code section to measure */
>     t += getnanotime();
>     /* ignore */
>   }
>   trace_performance(t, "frotz");

Hmph. Even though trace_performance() makes an extra call to getnanotime() in order to return, examples do not use the returned value? The second example is a good illustration why it makes sense for trace_performance_since(), though.

> +static void trace_performance_vfl(const char *file, int line,
> +				      uint64_t nanos, const char *format,
> +				      va_list ap)
> +{

Just being curious, but what does "v" stand for?

The "_fl" suffix you gave to printf family made a lot of sense to me, and I would have expected that this to be called with a "_flt" suffix, meaning "we have file, line and then time as extra parameters" or something.

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