Source: linux
Severity: wishlist


Hi.

Is there any reasons why you've enabled CONFIG_CC_OPTIMIZE_FOR_SIZE?

>From the help:
> Enabling this option will pass "-Os" instead of "-O2" to gcc resulting in a smaller kernel.

>From gcc:
> Optimize for size. -Os enables all -O2 optimizations that do not
> typically increase code size. It also performs further
> optimizations designed to reduce code size.
> -Os disables the following optimization flags: -falign-functions
> -falign-jumps -falign-loops -falign-labels -freorder-blocks
> -freorder-blocks-and-partition -fprefetch-loop-arrays
> -ftree-vect-loop-version


So we loose all kinds of optimisations just for storage, which really doesn't
count on all but embedded systems.


Cheers,
Chris.


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On Tue, Aug 14, 2012 at 09:56:17PM +0200, Christoph Anton Mitterer wrote:
> Source: linux
> Severity: wishlist
>
>
> Hi.
>
> Is there any reasons why you've enabled CONFIG_CC_OPTIMIZE_FOR_SIZE?

This is the recommended default (though not the actual default).

> >From gcc:
> > Optimize for size. -Os enables all -O2 optimizations that do not
> > typically increase code size. It also performs further
> > optimizations designed to reduce code size.
> > -Os disables the following optimization flags: -falign-functions
> > -falign-jumps -falign-loops -falign-labels -freorder-blocks
> > -freorder-blocks-and-partition -fprefetch-loop-arrays
> > -ftree-vect-loop-version
>
>
> So we loose all kinds of optimisations just for storage, which really doesn't
> count on all but embedded systems.

Larger code results in more I-cache misses, so it can be slower after
all.

Let's see your benchmark results.

Ben.

--
Ben Hutchings
We get into the habit of living before acquiring the habit of thinking.
- Albert Camus


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Hi Ben.


On Tue, 2012-08-14 at 21:57 +0100, Ben Hutchings wrote:
> > Is there any reasons why you've enabled CONFIG_CC_OPTIMIZE_FOR_SIZE?
> This is the recommended default (though not the actual default).
Just a wild guess, but the help text could have just not been updated
(as in many cases).

Anyway,.. I just wanted you to point on this


> Larger code results in more I-cache misses, so it can be slower after
> all.
> Let's see your benchmark results.
Well.. I guess making usable benchmarks there is really difficult,.. as
this likely also depends on the system usage, wouldn't it?


Cheers,
Chris.