[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20150412062015.GA8458@x4>
Date: Sun, 12 Apr 2015 08:20:15 +0200
From: Markus Trippelsdorf <markus@...ppelsdorf.de>
To: Ingo Molnar <mingo@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Jakub Jelinek <jakub@...hat.com>,
Denys Vlasenko <dvlasenk@...hat.com>,
Borislav Petkov <bp@...en8.de>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Andy Lutomirski <luto@...capital.net>,
Jason Low <jason.low2@...com>, Brian Gerst <brgerst@...il.com>,
Aswin Chandramouleeswaran <aswin@...com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Davidlohr Bueso <dave@...olabs.net>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"H. Peter Anvin" <hpa@...or.com>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86: Turn off GCC branch probability heuristics
On 2015.04.12 at 07:47 +0200, Ingo Molnar wrote:
>
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
>
> > On Sat, Apr 11, 2015 at 11:57 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> > >
> > > I thinks its just the no-guess one:
> > >
> > > text data dec patch reduction
> > > 7563475 1781048 10302987
> > > 7192973 1780024 9931461 no-guess -4.8%
> > > 7354819 1781048 958464 align-1 -2.7%
> > > 7192973 1780024 9931461 no-guess + align-1 -4.8%
> >
> > Yeah, a 5% code expansion is a big deal. Sadly, it looks like
> > 'no-guess' also disables our explicit likely/unlikely handling.
>
> So I spent some time trying to get as much code size reduction as
> possible via GCC optimization options, and the total savings possible
> are 10.1%:
>
> text data bss dec filename
> 12566391 1617840 1089536 15273767 vmlinux.vanilla
> 11416805 1617840 1089536 14124181 vmlinux.combo
> 10532552 1596080 1089536 13218168 vmlinux.Os
If you like to play with more knobs you could explore the various
--param options that are listed in the gcc man page...
--
Markus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists