From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTP id EC6C0DDF8B for ; Thu, 22 Mar 2007 23:06:39 +1100 (EST) Subject: Re: [RFC/PATCH] powerpc: Always use -mno-string & -mno-multiple From: Benjamin Herrenschmidt To: Segher Boessenkool In-Reply-To: <5fd8e208c5e6c87f852d6a528589dce3@kernel.crashing.org> References: <1174543838.10836.21.camel@localhost.localdomain> <5fd8e208c5e6c87f852d6a528589dce3@kernel.crashing.org> Content-Type: text/plain Date: Thu, 22 Mar 2007 23:06:31 +1100 Message-Id: <1174565191.10836.43.camel@localhost.localdomain> Mime-Version: 1.0 Cc: Akinobu Mita , Paul Mackerras , linuxppc-dev list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2007-03-22 at 13:02 +0100, Segher Boessenkool wrote: > > powerpc: Always use -mno-string and -mno-multiple > > > > The string and multiple load/store instructions are causing more > > damage than help on a lot of processors where they are microcoded > > and are generally no good for the kernel to use. Let's make sure > > we don't emit them on any powerpc variant. > > And they help a lot on many 32-bit CPUs. NAK. > > If you tell your GCC to compile for a certain CPU where > these insns would be very slow, GCC will automagically > not generate them, already. multiple do, strings really don't much except maybe on 601.... we don't quite yet have the options to compile for specific CPUs on arch/powerpc so -mno-string is a good idea generally, though I agree -mno-multiple isn't, thus my next patch :-) Ben.