Re: [PATCH 05/33] perf record: Allow the user to disable time stamps

From: Ingo Molnar
Date: Tue Aug 05 2014 - 02:09:08 EST



* Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:

> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
>

This patch looks dangerous and misleading to me.

> Time stamps are always implicitely enabled for record currently. The
> old --time/-T option is a nop.
>
> Allow the user to disable timestamps by using --no-time
>
> This can cause some minor misaccounting (by missing mmaps), but
> significantly lowers the size of perf.data

I'm not any big change in size:

-rw------- 1 mingo mingo 384768 Aug 5 08:01 perf.data.timestamps
-rw------- 1 mingo mingo 336952 Aug 5 08:00 perf.data.notimestamps

That's a ~14% reduction - it's certainly noticeable but not
earth-shattering.

And what is called 'minor misaccounting' in the description is
actually a potentially broken profile that people might rely on.

So the patch description misleads twice: by exaggerating the
advantages and also by downplaying the disadvantages.

So either remove the --time option altogether, or fix its
'misaccounting' so that the profile can be relied on.

Thanks,

Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/