From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932938Ab2CZQVI (ORCPT ); Mon, 26 Mar 2012 12:21:08 -0400 Received: from mail-we0-f174.google.com ([74.125.82.174]:54750 "EHLO mail-we0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932655Ab2CZQVG (ORCPT ); Mon, 26 Mar 2012 12:21:06 -0400 Date: Mon, 26 Mar 2012 18:21:01 +0200 From: Ingo Molnar To: Avi Kivity Cc: Benjamin Herrenschmidt , Linus Torvalds , linux-kernel , KVM list , Marcelo Tosatti , Paul Mackerras , Alexander Graf Subject: Re: [GIT PULL] KVM updates for the 3.4 merge window Message-ID: <20120326162101.GA524@gmail.com> References: <4F688F48.6090303@redhat.com> <1332461414.2982.90.camel@pasglop> <4F6EEEC1.4030608@redhat.com> <1332708684.2882.24.camel@pasglop> <4F703F5E.8030700@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F703F5E.8030700@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Avi Kivity wrote: > Say a fix comes in which needs to be mainlined during -rc. So > I put it in some other branch, to be sent off to Linus in a > few days after maturing a little. Meanwhile developers see an > incomplete tree, since that patch is not in it. > > Once Linus pulls, I can merge it back (or even before, if I'm > reasonably certain it's not going to change), but it leaves a > history of unneeded merges. Or we can do throwaway merges > like tip.git. We don't do throwaway merges in the -tip development branches themselves, i.e. in tip:sched/core, tip:perf/core, tip:timers/core, etc. When a fix goes into tip:sched/urgent then until Linus merges it it's not in tip:sched/core. 99% of the fixes don't *have to* go into sched/core straight away. In the odd case where there's some dependency, we can manually merge it into tip:sched/core ahead of Linus pulling into an -rc. Those rare merges are not a problem, and I explain the reason in the merge commit itself. If you look at: gll v3.2..v3.3 | grep -E '/urgent.*/core' you'll see that I only had to do it once in the previous cycle: d6c1c49de577 Merge branch 'perf/urgent' into perf/core and the changelog explains the background: Merge reason: Add these cherry-picked commits so that future changes on perf/core don't conflict. it was a rare, oddball situation where we cherry-picked perf/core changes into perf/urgent. Extra merges are perfectly fine in that case. The 'throwaway' tip:master branch you are probably referring to is basically just a testing branch, a convenient merged tree of the one dozen maintainer trees that are hosted in -tip. Since we don't want to force Linus's hand of him being able to reject individual trees we don't merge them properly - hence the integrated tree is a throwaway tree in theory. In practice I tend to throw it away only once per cycle, around -rc1, once all pending trees went to Linus. tip:master is not used for any Git based contribution work - it's for testing, it's for people who want to work with patches - the commits themselves always go into persistent non-rebasing, append-only Git trees. If we mess up bisectability we do a delta fix. When choosing between somewhat better bisectability and a proper history that others can rely on then proper history wins hands down. Thanks, Ingo