From: Martin Bligh <mbligh@mbligh.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Linus Torvalds <torvalds@osdl.org>,
Matt Mackall <mpm@selenic.com>,
Arjan van de Ven <arjan@infradead.org>,
Chuck Ebbert <76306.1226@compuserve.com>,
Adrian Bunk <bunk@stusta.de>, Andrew Morton <akpm@osdl.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Dave Jones <davej@redhat.com>,
Tim Schmielau <tim@physik3.uni-rostock.de>
Subject: Re: [patch 00/2] improve .text size on gcc 4.0 and newer compilers
Date: Thu, 05 Jan 2006 16:55:01 -0800 [thread overview]
Message-ID: <43BDBFE5.5020405@mbligh.org> (raw)
In-Reply-To: <20060106004050.GA18727@elte.hu>
> these 30 functions involve roughly 10-15 .o files, so we've got 2-3
> functions per .o file only. And that's typical for VFS, IO, networking
> and lots of other syscall types. So if the full kernel image is 3MB, and
> we've got 30 functions totalling to 3000 bytes, they are spread out in
> 10-15 groups right now - creating 10-15 split icache lines. (in reality
> we have in excess of 20 split icache-lines, due to weak cohesion even
> within .o files) With 64-byte lines that's 320-480 bytes 'lost' due to
> fragmentation alone, with 128-byte lines it's 640-960 bytes - which is
> 10%-21% in the 64-byte case, and 21%-42% in the 128-byte case. I.e. the
> icache bloat just due to the placement is quite significant. Adding
> .o-level fragmentation plus inter-function inactive code to the mix can
> easily baloon this even higher. Plus the current method of doing
> unlikely() means the unlikely instructions are near the end of the
> function - so they still 'spread apart' the footprint and thus have a
> nontrivial icache cost.
mmm. will take me a little time to digest that.
But we were just discussing here ... wouldn't it be worth moving
"unlikely" sections of code completely out of line? If they were calls
to separate functions, all this optimisation stuff could just work at a
function level, and would be pretty trivial to do?
ie instead of:
if (unlikely(conditon)) {
do;
some;
stuff;
BUG();
error();
oh_dear();
}
we'd have
if (unlikely(conditon)) {
call_oh_shit();
}
__rarely_called void call_oh_shit()
{
do;
some;
stuff;
BUG();
error();
oh_dear();
}
depends how long they are, I suppose. Moving that out of line would seem
to make more difference to icache footprint to me than just cacheline
packing functions.
M.
next prev parent reply other threads:[~2006-01-06 0:57 UTC|newest]
Thread overview: 167+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-05 0:55 [patch 00/2] improve .text size on gcc 4.0 and newer compilers Chuck Ebbert
2006-01-05 1:07 ` Martin Bligh
2006-01-05 12:19 ` Arjan van de Ven
2006-01-05 14:30 ` Jakub Jelinek
2006-01-05 16:55 ` Linus Torvalds
2006-01-05 18:42 ` Daniel Jacobowitz
2006-01-05 17:02 ` Matt Mackall
2006-01-05 17:59 ` Martin Bligh
2006-01-05 18:09 ` Arjan van de Ven
2006-01-05 18:43 ` Daniel Jacobowitz
2006-01-05 19:17 ` Linus Torvalds
2006-01-05 19:40 ` Linus Torvalds
2006-01-05 19:49 ` Martin Bligh
2006-01-05 20:13 ` Linus Torvalds
2006-01-05 20:15 ` Linus Torvalds
2006-01-05 23:30 ` Ingo Molnar
2006-01-05 23:54 ` Linus Torvalds
2006-01-06 0:15 ` Ingo Molnar
2006-01-06 0:27 ` Linus Torvalds
2006-01-06 0:54 ` Ingo Molnar
2006-01-06 0:02 ` Martin Bligh
2006-01-06 0:40 ` Ingo Molnar
2006-01-06 0:55 ` Martin Bligh [this message]
2006-01-06 1:48 ` Mitchell Blank Jr
2006-01-06 0:50 ` Mitchell Blank Jr
2006-01-06 0:58 ` Ingo Molnar
2006-01-06 1:22 ` Mitchell Blank Jr
2006-01-05 21:34 ` Matt Mackall
2006-01-05 22:08 ` Linus Torvalds
2006-01-05 22:36 ` Matt Mackall
2006-01-05 22:49 ` Martin Bligh
2006-01-05 23:02 ` Matt Mackall
2006-01-05 22:55 ` Ingo Molnar
2006-01-05 23:11 ` Matt Mackall
2006-01-05 23:27 ` Jesse Barnes
2006-01-05 23:58 ` Ingo Molnar
2006-01-05 21:32 ` Grzegorz Kulewski
-- strict thread matches above, loose matches on Subject: below --
2005-12-28 11:46 Ingo Molnar
2005-12-28 19:17 ` Linus Torvalds
2005-12-28 19:34 ` Arjan van de Ven
2005-12-28 21:02 ` Linus Torvalds
2005-12-28 21:17 ` Arjan van de Ven
2005-12-28 21:23 ` Ingo Molnar
2005-12-28 21:48 ` Ingo Molnar
2005-12-28 23:56 ` Krzysztof Halasa
2005-12-29 7:41 ` Ingo Molnar
2005-12-29 8:02 ` Dave Jones
2005-12-29 19:44 ` Krzysztof Halasa
2005-12-29 4:11 ` Andrew Morton
2005-12-29 7:32 ` Ingo Molnar
2005-12-29 14:58 ` Horst von Brand
2005-12-29 15:40 ` Adrian Bunk
2005-12-29 17:41 ` Linus Torvalds
2005-12-29 18:42 ` Arjan van de Ven
2005-12-29 18:45 ` Arjan van de Ven
2005-12-29 20:19 ` Ingo Molnar
2005-12-29 22:20 ` Matt Mackall
2005-12-29 20:28 ` Dave Jones
2005-12-29 20:49 ` Linus Torvalds
2005-12-29 21:25 ` Linus Torvalds
[not found] ` <20051229224839.GA12247@elte.hu>
2005-12-29 22:58 ` Arjan van de Ven
2005-12-30 2:03 ` Tim Schmielau
2005-12-30 2:15 ` Tim Schmielau
2005-12-30 7:49 ` Ingo Molnar
2005-12-31 14:38 ` Adrian Bunk
2005-12-31 14:45 ` Ingo Molnar
2005-12-31 15:08 ` Adrian Bunk
2006-01-02 10:37 ` Ingo Molnar
2006-01-02 10:48 ` Arjan van de Ven
2006-01-02 13:43 ` Adrian Bunk
2006-01-02 14:05 ` Ingo Molnar
2006-01-02 15:01 ` Adrian Bunk
2006-01-02 18:44 ` Krzysztof Halasa
2006-01-02 18:51 ` Arjan van de Ven
2006-01-02 19:49 ` Krzysztof Halasa
2006-01-02 19:54 ` Arjan van de Ven
2006-01-02 20:05 ` Krzysztof Halasa
2006-01-02 20:18 ` Jörn Engel
2006-01-02 22:23 ` Russell King
2006-01-02 23:55 ` Alan Cox
2006-01-03 3:59 ` Daniel Jacobowitz
2006-01-03 8:53 ` Russell King
2006-01-03 8:56 ` Arjan van de Ven
2006-01-03 9:00 ` Russell King
2006-01-03 9:10 ` Arjan van de Ven
2006-01-03 9:14 ` Vitaly Wool
2006-01-02 19:03 ` Andrew Morton
2006-01-02 19:17 ` Jakub Jelinek
2006-01-02 19:30 ` Andrew Morton
2006-01-02 19:41 ` Linus Torvalds
2006-01-02 19:53 ` Ingo Molnar
2006-01-02 20:28 ` Jakub Jelinek
2006-01-02 20:09 ` Ingo Molnar
2006-01-02 20:24 ` Andrew Morton
2006-01-02 20:40 ` Ingo Molnar
2006-01-02 20:30 ` Ingo Molnar
2006-01-02 19:12 ` Linus Torvalds
2006-01-02 19:59 ` Krzysztof Halasa
2006-01-02 20:13 ` Ingo Molnar
2006-01-02 21:00 ` Jan Engelhardt
2006-01-02 22:43 ` Linus Torvalds
2006-01-02 13:42 ` Adrian Bunk
2006-01-02 18:28 ` Andrew Morton
2006-01-02 18:49 ` Arjan van de Ven
2006-01-02 19:26 ` Jörn Engel
2006-01-02 21:51 ` Grant Coady
2006-01-02 22:03 ` Antonio Vargas
2006-01-02 22:56 ` Arjan van de Ven
2006-01-02 23:10 ` Grant Coady
2006-01-02 23:57 ` Alan Cox
2006-01-02 23:58 ` Grant Coady
2006-01-03 5:31 ` Nick Piggin
2006-01-03 23:40 ` Martin J. Bligh
2006-01-04 4:28 ` Matt Mackall
2006-01-04 5:51 ` Martin J. Bligh
2006-01-04 17:10 ` Matt Mackall
2006-01-04 22:37 ` Linus Torvalds
2006-01-05 0:55 ` Martin Bligh
2006-01-04 17:36 ` Zwane Mwaikambo
2005-12-31 3:51 ` Kurt Wall
2005-12-30 3:31 ` Nicolas Pitre
2005-12-30 3:47 ` Mark Lord
2005-12-30 3:56 ` Dave Jones
2005-12-30 3:57 ` Mark Lord
2005-12-30 4:02 ` Dave Jones
2005-12-30 4:11 ` Mark Lord
2005-12-30 4:14 ` Mark Lord
2005-12-30 4:20 ` Mark Lord
2005-12-30 5:04 ` Dave Jones
2005-12-29 23:16 ` Willy Tarreau
2005-12-30 8:05 ` Arjan van de Ven
2005-12-30 8:15 ` Willy Tarreau
2005-12-30 8:24 ` Arjan van de Ven
2005-12-30 9:20 ` Willy Tarreau
2005-12-30 13:38 ` Adrian Bunk
2005-12-30 8:33 ` Jesper Juhl
2005-12-30 9:28 ` Willy Tarreau
2005-12-30 9:37 ` Jesper Juhl
2005-12-30 9:38 ` Willy Tarreau
2005-12-30 19:53 ` Alistair John Strachan
2005-12-29 7:49 ` Arjan van de Ven
2005-12-29 15:01 ` Horst von Brand
2005-12-30 15:28 ` Alan Cox
2005-12-30 20:59 ` Adrian Bunk
2005-12-30 22:12 ` Matt Mackall
2005-12-30 23:54 ` Adrian Bunk
2005-12-31 9:20 ` Arjan van de Ven
2005-12-29 14:38 ` Christoph Hellwig
2005-12-29 14:54 ` Arjan van de Ven
2005-12-29 15:35 ` Adrian Bunk
2005-12-29 15:38 ` Arjan van de Ven
2005-12-29 15:42 ` Jakub Jelinek
2005-12-29 19:14 ` Adrian Bunk
2005-12-30 9:28 ` Andi Kleen
2005-12-30 9:40 ` Ingo Molnar
2005-12-30 10:14 ` Ingo Molnar
2005-12-30 13:31 ` Adrian Bunk
2005-12-30 14:08 ` Christian Trefzer
2005-12-30 10:25 ` Andi Kleen
2005-12-29 0:37 ` Rogério Brito
2006-01-03 3:36 ` Daniel Jacobowitz
2005-12-29 4:38 ` Adrian Bunk
2005-12-29 7:59 ` Ingo Molnar
2005-12-29 13:52 ` Adrian Bunk
2005-12-29 19:57 ` Horst von Brand
2005-12-29 20:25 ` Ingo Molnar
2005-12-31 15:22 ` Adrian Bunk
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