From: Ingo Molnar <mingo@elte.hu>
To: Pekka Enberg <penberg@kernel.org>
Cc: Jesper Juhl <jj@chaosbits.net>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Daniel Lezcano <daniel.lezcano@free.fr>,
Eric Paris <eparis@redhat.com>,
Roman Zippel <zippel@linux-m68k.org>,
linux-kbuild@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: PATCH][RFC][resend] CC_OPTIMIZE_FOR_SIZE should default to N
Date: Tue, 22 Mar 2011 11:27:41 +0100 [thread overview]
Message-ID: <20110322102741.GA4448@elte.hu> (raw)
In-Reply-To: <AANLkTinmAJsXy=iJ5Fq-+CLTAGXTtLGhULRUf=Q1rkY1@mail.gmail.com>
* Pekka Enberg <penberg@kernel.org> wrote:
> Hi Jesper,
>
> On Mon, Mar 21, 2011 at 10:08 PM, Jesper Juhl <jj@chaosbits.net> wrote:
> > I believe that the majority of systems we are built on want a -O2 compiled
> > kernel. Optimizing for size (-Os) is mainly benneficial for embedded
> > systems and systems with very small CPU caches (correct me if I'm wrong).
>
> Please take a look at commit 0910b44 ("Expose "Optimize for size"
> option for everybody") for the reasoning behind defaulting to -Os.
If that situation has changed - if GCC has regressed in this area then a commit
changing the default IMHO gains a lot of credibility if it is backed by careful
measurements using perf stat --repeat or similar tools.
See the hard numbers in this upstream commit for example:
ea7145477a46: x86: Separate out entry text section
there we were able to prove the positive effects of a pretty subtle change to
the layout of the instruction cache, with a measurement noise in the 0.1%
range.
Thanks,
Ingo
next prev parent reply other threads:[~2011-03-22 10:27 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-21 20:08 PATCH][RFC][resend] CC_OPTIMIZE_FOR_SIZE should default to N Jesper Juhl
2011-03-22 2:52 ` Steven Rostedt
2011-03-22 8:21 ` Pekka Enberg
2011-03-22 8:25 ` Jesper Juhl
2011-03-22 10:27 ` Ingo Molnar [this message]
2011-03-22 16:59 ` Linus Torvalds
2011-03-23 17:45 ` Andi Kleen
2011-03-23 21:14 ` Ingo Molnar
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