linux-kernel - Re: [PATCH] lib/vsprintf: add %pT[C012] format specifier

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Message-ID: <CAMuHMdV13i8VicysHjKMmQtf+ZXCcCV+KiBVEnBONuf4=1w9_Q@mail.gmail.com>
Date:	Tue, 7 Jan 2014 19:28:54 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Pavel Machek <pavel@....cz>
Cc:	Joe Perches <joe@...ches.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/vsprintf: add %pT[C012] format specifier

On Tue, Jan 7, 2014 at 6:56 PM, Pavel Machek <pavel@....cz> wrote:
>> The additional cost of using current vs NULL is ~zero.
>
> The additional cost of current vs NULL is cca 8 bytes per caller. Test
> for NULL is cca 4 bytes, maybe 20 bytes total. I believe it is worth
> it.

It depends (typical answer ;-)

On architectures that keep current in a register, the cost of using it is
usually zero, as there's typically no difference between pushing a register
or a zero on the stack, or moving a register or a zero to another register.

current_thread_info()->task is more expensive.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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