From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: Index/hash order Date: Thu, 14 Apr 2005 09:04:22 +0200 Message-ID: <20050414070422.GA3226@elte.hu> References: <20050412230027.GA21759@elte.hu> <20050412230729.GA22179@elte.hu> <20050413111355.GB13865@elte.hu> <425D4E1D.4040108@zytor.com> <20050413165310.GA22428@elte.hu> <425D4FB1.9040207@zytor.com> <87aco2gxu2.fsf@deneb.enyo.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Florian Weimer , "H. Peter Anvin" , git@vger.kernel.org X-From: git-owner@vger.kernel.org Thu Apr 14 09:01:47 2005 Return-path: Received: from vger.kernel.org ([12.107.209.244]) by ciao.gmane.org with esmtp (Exim 4.43) id 1DLyLo-0001xD-Mv for gcvg-git@gmane.org; Thu, 14 Apr 2005 09:01:20 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261445AbVDNHEh (ORCPT ); Thu, 14 Apr 2005 03:04:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261444AbVDNHEh (ORCPT ); Thu, 14 Apr 2005 03:04:37 -0400 Received: from mx1.elte.hu ([157.181.1.137]:40372 "EHLO mx1.elte.hu") by vger.kernel.org with ESMTP id S261445AbVDNHEd (ORCPT ); Thu, 14 Apr 2005 03:04:33 -0400 Received: from chiara.elte.hu (chiara.elte.hu [157.181.150.200]) by mx1.elte.hu (Postfix) with ESMTP id 0432431D0B1; Thu, 14 Apr 2005 09:03:50 +0200 (CEST) Received: by chiara.elte.hu (Postfix, from userid 17806) id 8773A1FC2; Thu, 14 Apr 2005 09:04:25 +0200 (CEST) To: Linus Torvalds Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-ELTE-SpamVersion: MailScanner 4.31.6-itk1 (ELTE 1.2) SpamAssassin 2.63 ClamAV 0.73 X-ELTE-VirusStatus: clean X-ELTE-SpamCheck: no X-ELTE-SpamCheck-Details: score=-4.9, required 5.9, autolearn=not spam, BAYES_00 -4.90 X-ELTE-SpamLevel: X-ELTE-SpamScore: -4 Sender: git-owner@vger.kernel.org Precedence: bulk X-Mailing-List: git@vger.kernel.org * Linus Torvalds wrote: > > I've run a few tests, just to get a few numbers of the overhead > > involved. I used the last ~8,000 changesets from the BKCVS kernel > > repository. With cold cache, a checkout from cold cache takes about > > 250 seconds on my laptop. I don't have git numbers, but a mere copy > > of the kernel tree needs 40 seconds. > > I will bet you that a git checkout is _faster_ than a kernel source > tree copy. The time will be dominated by the IO costs (in particular > the read costs), and the IO costs are lower thanks to compression. So > I think that the cold-cache case will beat your 40 seconds by a clear > margin. It generally compresses to half the size, so 20 seconds is not > impossible (although seek costs would tend to stay constant, so I'd > expect it to be somewhere in between the two). i'd be surprised if it was twice as fast - cache-cold linear checkouts are _seek_ limited, and it doesnt matter whether after a 1-2 msec track-to-track disk seek the DMA engine spends another 30 microseconds DMA-ing 60K uncompressed data instead of 30K compressed... (there are other factors, but this is the main thing.) Ingo