eliminate -pipe from kernel compile

eliminate -pipe from kernel compile

[Lance Tagliapietra]

Hello,

I was noticing that kernel compiling is set up to have gcc pipe data from one pass to another, instead of using 
temporary files.  On a memory constrained environment, this may not be the best idea (or at least I'd like to
explore that idea).  Instead of loading the assember, and having immediately being swapped out while the cc1 pass 
runs, it may make more sense to have the temp files being written, instead of the swap in and out, when compiling 
the various objects of the kernel.

So, simply pulling out the -pipe from the compiler flag list didn't see to have the desired effect.  I'm afraid I'm 
still missing something.  I'm still observing the assembler being loaded.

Thoughts?

Thanks,

--Lance

Re: eliminate -pipe from kernel compile

[Geert Uytterhoeven]

Added linux-kbuild

On Mon, May 11, 2009 at 03:58, Lance Tagliapietra <lancetag@luminet.net> wrote:
> I was noticing that kernel compiling is set up to have gcc pipe data from one pass to another, instead of using
> temporary files.  On a memory constrained environment, this may not be the best idea (or at least I'd like to
> explore that idea).  Instead of loading the assember, and having immediately being swapped out while the cc1 pass
> runs, it may make more sense to have the temp files being written, instead of the swap in and out, when compiling
> the various objects of the kernel.
>
> So, simply pulling out the -pipe from the compiler flag list didn't see to have the desired effect.  I'm afraid I'm
> still missing something.  I'm still observing the assembler being loaded.
>
> Thoughts?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds
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Re: eliminate -pipe from kernel compile

[Sam Ravnborg]

On Mon, May 11, 2009 at 08:02:16AM +0200, Geert Uytterhoeven wrote:
> Added linux-kbuild
> 
> On Mon, May 11, 2009 at 03:58, Lance Tagliapietra <lancetag@luminet.net> wrote:
> > I was noticing that kernel compiling is set up to have gcc pipe data from one pass to another, instead of using
> > temporary files.  On a memory constrained environment, this may not be the best idea (or at least I'd like to
> > explore that idea).  Instead of loading the assember, and having immediately being swapped out while the cc1 pass
> > runs, it may make more sense to have the temp files being written, instead of the swap in and out, when compiling
> > the various objects of the kernel.
> >
> > So, simply pulling out the -pipe from the compiler flag list didn't see to have the desired effect.  I'm afraid I'm
> > still missing something.  I'm still observing the assembler being loaded.

1) How did you "pulling out the -pipe from the compiler flag list"?
Please show this as a patch.

2) Did you verify that -pipe was used before and no more after your
   changes?
   Hint - use "make V=1" to see all command line options to gcc

	Sam
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Re: eliminate -pipe from kernel compile

[Lance Tagliapietra]

Hello,

I just completed a test build with my patch to arch/m68k/Makefile to remove the -pipe flag (see patch below).  
Watching the build confirmed that a) -pipe was no longer showing up in the gcc command lines and b) temporary 
files were being created as expected without pipe; and c) the as command was not loaded waiting for cc1 to 
complete.  Yea!  The /arch/m68k/Makefile is the only place where the -pipe flag is located, and that seems
to be the place for all arch's.

--- arch/m68k/Makefile.old	2009-05-13 21:58:28.000000000 -0500
+++ arch/m68k/Makefile	2009-05-09 11:16:39.000000000 -0500
@@ -33,7 +33,9 @@
 CHECKFLAGS += -D__mc68000__
 
 # without -fno-strength-reduce the 53c7xx.c driver fails ;-(
-KBUILD_CFLAGS += -pipe -fno-strength-reduce -ffixed-a2
+# delete -pipe to save RAM / minimize swap during compile
+# original: KBUILD_CFLAGS += -pipe -fno-strength-reduce -ffixed-a2
+KBUILD_CFLAGS += -fno-strength-reduce -ffixed-a2
 
 # enable processor switch if compiled only for a single cpu
 ifndef CONFIG_M68020

Pulling out the -pipe does seem to cut compile time.  I am working on hard numbers.

--Lance

On Wed, May 13, 2009 at 02:38:29AM +0200, Sam Ravnborg wrote:
> On Mon, May 11, 2009 at 08:02:16AM +0200, Geert Uytterhoeven wrote:
> > Added linux-kbuild
> > 
> > On Mon, May 11, 2009 at 03:58, Lance Tagliapietra <lancetag@luminet.net> wrote:
> > > I was noticing that kernel compiling is set up to have gcc pipe data from one pass to another, instead of using
> > > temporary files. ?On a memory constrained environment, this may not be the best idea (or at least I'd like to
> > > explore that idea). ?Instead of loading the assember, and having immediately being swapped out while the cc1 pass
> > > runs, it may make more sense to have the temp files being written, instead of the swap in and out, when compiling
> > > the various objects of the kernel.
> > >
> > > So, simply pulling out the -pipe from the compiler flag list didn't see to have the desired effect. ?I'm afraid I'm
> > > still missing something. ?I'm still observing the assembler being loaded.
> 
> 1) How did you "pulling out the -pipe from the compiler flag list"?
> Please show this as a patch.
> 
> 2) Did you verify that -pipe was used before and no more after your
>    changes?
>    Hint - use "make V=1" to see all command line options to gcc
> 
> 	Sam