From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from fed1rmmtao03.cox.net (fed1rmmtao03.cox.net [68.230.241.36]) by ozlabs.org (Postfix) with ESMTP id E382867B33 for ; Fri, 6 May 2005 02:29:31 +1000 (EST) Date: Thu, 5 May 2005 09:29:25 -0700 From: Tom Rini To: Kumar Gala Message-ID: <20050505162925.GB1221@smtp.west.cox.net> References: <20050505152709.GA1221@smtp.west.cox.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: Cc: linuxppc-dev@ozlabs.org Subject: Re: [PATCH] Set cpu explicitly in kernel compiles List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, May 05, 2005 at 11:22:38AM -0500, Kumar Gala wrote: > > On May 5, 2005, at 10:27 AM, Tom Rini wrote: > > >On Thu, May 05, 2005 at 10:12:42AM -0500, Kumar Gala wrote: > > > > >> On May 5, 2005, at 9:23 AM, Tom Rini wrote: > > > > >> >On Thu, May 05, 2005 at 09:00:50AM -0500, Kumar Gala wrote: > > > > > > > > >> On May 5, 2005, at 7:24 AM, Dan Malek wrote: > > > > > > > > >> > > > > > > > > > > > > >On May 5, 2005, at 1:22 AM, Paul Mackerras wrote: > > > > > > > If you think we should have -mcpu=xxx on the command line > >for > >> >4xx, > > > > > > > 44x, 8xx, etc., then that's fine, but that is a separate > >problem > > > >> >from > > > > > > > what my patch was addressing (one which my patch might make > >it > > > >> >easier > > > > > > > to fix, though). > > > > > > > > > > > >I think that is exactly what we want, although I don't know how > >> >that is > > > > > > separate from the patch you sent.? My original comment was the > >> >patch > > > > > > fixes the problem for only one of the cpu cores, not all of > >them.? > > > >> >Which > > > > > > then led into the subsequent suggestion of making the biarch > >work > > > > > > like the past compilers, and we must specific the flags for > >POWER4 > > > > > > instead of the other way around.? Without explicit -mcpu > >flags, > >> >the > > > > > > existing compiler behavior is just fine .....? but, I guess > >I'd be > > > > > >standing > > > > > > in the way of progress to want this :-) > > > > > > > > >> I agree with Dan here.? I think we should go ahead and extend the > >> >patch > > > >> to set -mcpu and -mtune flags for the list of processors we have > >in > > > >> "Processor Type".? If I'm building a kernel for e500 or 4xx I > >might > >> >as > > > >> well get a kernel that is tuned a bit more for the subarch.? > > > > > > > > This is fine. > >> > > > > >> Additionally, there should be some expert override ability, so > >if I > > > >> really want to do -mcpu=7455 -mtune=7455 I can. > > > > > > > >Gack, no!? It's quite a pain to go from CONFIG_FOO="string" into > >> >useable > > > > Makefile bits that the one we did have back in 2.4 is gone.? That > >also > > > > implies gcc finally knows something about these cores that might > >be > > > > useful, which I don't think is the case, nor is it likely to be.? > >But > >> >if > > > > we did want it, we'd probably go the route x86 has. > > > > >> I'm not saying it has to be done via a CONFIG option, all I'm saying > >is > >> if I want to explicitly use GCC then I would hope we could somehow > >> disable it being override. > > > >If you're not doing it via CONFIG, that leaves manual (which is always > > an option) or seeing if passing CFLAGS on the cmdline overrides > >things, > > or adds to them. > > Thats all I really want. Just for us to make sure if I want to do > -mcpu=7455 -mtune=7455 I'm able to and it actually does what I told it > to do. I'm not sure if GCC is consistent on how it handles args that > are duplicated. For example what will happen with the following: > > gcc -mcpu=750 -mtune=7450 -mcpu=603 -mtune=603 > > Is this -mcpu=750 -mtune=7450 or -mcpu=603 -mtune=603 Last one wins, modulo gcc bugs, is the rule I believe. -- Tom Rini http://gate.crashing.org/~trini/