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Date: Fri, 8 Oct 2004 16:30:31 +0200 (CEST)
From: Grzegorz Kulewski <kangur@polcom.net>
To: Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua>
Cc: Andi Kleen <ak@muc.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Make gcc -align options .config-settable
In-Reply-To: <200410081710.58766.vda@port.imtp.ilyichevsk.odessa.ua>
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On Fri, 8 Oct 2004, Denis Vlasenko wrote:

> On Friday 08 October 2004 12:20, Andi Kleen wrote:
>> Denis Vlasenko <vda@port.imtp.ilyichevsk.odessa.ua> writes:
>>> Resend.
>>>
>>> With all alignment options set to 1 (minimum alignment),
>>> I've got 5% smaller vmlinux compared to one built with
>>> default code alignment.
>>>
>>> Rediffed against 2.6.9-rc3.
>>> Please apply.
>>
>> I agree with the basic idea (the big alignments also always annoy
>> me when I look at disassembly), but I think your CONFIG options
>> are far too complicated. I don't think anybody will go as far as
>> to tune loops vs function calls.
>>
>> I would just do a single CONFIG_NO_ALIGNMENTS that sets everything to
>> 1, that should be enough.
>
> For me, yes, but there are people which are slightly less obsessed
> with code size than me.
>
> They might want to say "try to align to 16 bytes if
> it costs less than 5 bytes" etc.
>
> Also bencmarking people may do little research on real usefulness of
> various kinds of alignment.

I think that removing aligns completly will be very bad. I am Gentoo user 
and I set my user space CFLAGS for all system to -falign-loops 
-fno-align-<everything else>. I did not tested it in depth, but my simple 
tests show that unaligning loops is a very bad idea. Unaligning functions 
is safer since small and fast functions should be always inlined.


Thanks,

Grzegorz Kulewski

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