Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423494Ab3FURSQ (ORCPT ); Fri, 21 Jun 2013 13:18:16 -0400 Received: from relay1.sgi.com ([192.48.179.29]:49473 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423152Ab3FURSO (ORCPT ); Fri, 21 Jun 2013 13:18:14 -0400 Message-ID: <51C48ADD.207@sgi.com> Date: Fri, 21 Jun 2013 12:18:21 -0500 From: Nathan Zimmer User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: "H. Peter Anvin" CC: Greg KH , , , , , , , , , , Subject: Re: [RFC 0/2] Delay initializing of large sections of memory References: <1371831934-156971-1-git-send-email-nzimmer@sgi.com> <20130621165142.GA32125@kroah.com> <51C48745.9030304@zytor.com> In-Reply-To: <51C48745.9030304@zytor.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [128.162.233.140] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2423 Lines: 58 On 06/21/2013 12:03 PM, H. Peter Anvin wrote: > On 06/21/2013 09:51 AM, Greg KH wrote: >> On Fri, Jun 21, 2013 at 11:25:32AM -0500, Nathan Zimmer wrote: >>> This rfc patch set delays initializing large sections of memory until we have >>> started cpus. This has the effect of reducing startup times on large memory >>> systems. On 16TB it can take over an hour to boot and most of that time >>> is spent initializing memory. >>> >>> We avoid that bottleneck by delaying initialization until after we have >>> started multiple cpus and can initialize in a multithreaded manner. >>> This allows us to actually reduce boot time rather then just moving around >>> the point of initialization. >>> >>> Mike and I have worked on this set for a while, with him doing the most of the >>> heavy lifting, and are eager for some feedback. >> Why make this a config option at all, why not just always do this if the >> memory size is larger than some specific number (like 8TB?) >> >> Otherwise the distros will always enable this option, and having it be a >> configuration choice doesn't make any sense. >> > Since you made it a compile time option, it would be good to know how > much code it adds, but otherwise I agree with Greg here... this really > shouldn't need to be an option. It *especially* shouldn't need to be a > hand-set runtime option (which looks quite complex, to boot.) The patchset as a whole is just over 400 lines so it doesn't add alot. If I were to pull the .config option it would probably remove 30 lines. The command line option is too complex but some of the data I haven't found a way to get at runtime yet. > > I suspect the cutoff for this should be a lot lower than 8 TB even, more > like 128 GB or so. The only concern is to not set the cutoff so low > that we can end up running out of memory or with suboptimal NUMA > placement just because of this. Even at lower amounts of ram there is an positive impact.I it knocks time off boot even at as small as a 1TB of ram. > Also, in case it is not bloody obvious: whatever memory the kernel image > was loaded into MUST be considered "online", even if it is loaded way high. > > -hpa > > > > Ok -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/