From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Fri, 4 Jan 2008 16:27:00 +0000 From: Alan Cox Subject: Re: [patch] i386: avoid expensive ppro ordering workaround for default 686 kernels Message-ID: <20080104162700.3aef1806@lxorguk.ukuu.org.uk> In-Reply-To: <20080103231017.GA25880@wotan.suse.de> References: <20071222005737.2675c33b.akpm@linux-foundation.org> <20071223055730.GA29288@wotan.suse.de> <20071222223234.7f0fbd8a.akpm@linux-foundation.org> <20071223071529.GC29288@wotan.suse.de> <20080101234133.4a744329@the-village.bc.nu> <20080102110225.GA16154@wotan.suse.de> <20080102134433.6ca82011@the-village.bc.nu> <20080103041708.GB26487@wotan.suse.de> <20080103142330.111d4067@lxorguk.ukuu.org.uk> <20080103231017.GA25880@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Linus Torvalds , Andrew Morton , Hugh Dickins , Linux Memory Management List , Benjamin Herrenschmidt List-ID: > > The cost on a 586 SMP box (ie pentium) is basically nil. All cross CPU > > transactions are hideously slow anyway locked or not. > > That's wrong. Firstly, spinlocks are very often retaken by the same CPU, and they Go time it. It certainly used to be the case. > On 586 SMP systems, didn't lock ops actually go out on the bus, and hence are much > more expensive than they are today (although today they are still one or two orders > of magnitude more expensive than regular memory ops). All cross CPU cache stuff goes that way, not that may P5 SMP boxes are running today except in Mr Bottomley's residence. > And if you build a kernel which is to support 686, PII, and later, you don't want > them by default either, most probably. I want a kernel for VIA C3 or later which happens to include K6 (still common), PII+ and maybe not PPro. So your patch should go in the bitbucket by the sound of it and Adrian's get merged. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org