From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752185AbbJEDi0 (ORCPT ); Sun, 4 Oct 2015 23:38:26 -0400 Received: from mx2.suse.de ([195.135.220.15]:54911 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751975AbbJEDiZ (ORCPT ); Sun, 4 Oct 2015 23:38:25 -0400 Date: Sun, 4 Oct 2015 20:37:08 -0700 From: Davidlohr Bueso To: Geliang Tang Cc: Andrew Morton , "Kirill A. Shutemov" , Hugh Dickins , "Peter Zij lstra (Intel)" , Andrea Arcangeli , Joonsoo Kim , Arnd Bergmann , Paul Gortmaker , Leon Romanovsky , Oleg Nesterov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/3] mm/nommu: drop unlikely behind BUG_ON() Message-ID: <20151005033708.GC8831@linux-uzut.site> Mail-Followup-To: Geliang Tang , Andrew Morton , "Kirill A. Shutemov" , Hugh Dickins , "Peter Zij lstra (Intel)" , Andrea Arcangeli , Joonsoo Kim , Arnd Bergmann , Paul Gortmaker , Leon Romanovsky , Oleg Nesterov , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <45bf632d263280847a2a894017c62b7f2a71eda1.1443937856.git.geliangtang@163.com> <20151005015055.GA8831@linux-uzut.site> <20151005023000.GA1607@bogon> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20151005023000.GA1607@bogon> 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 On Mon, 05 Oct 2015, Geliang Tang wrote: >On Sun, Oct 04, 2015 at 06:50:55PM -0700, Davidlohr Bueso wrote: >> On Sun, 04 Oct 2015, Geliang Tang wrote: >> >> >BUG_ON() already contain an unlikely compiler flag. Drop it. >> > >> >Signed-off-by: Geliang Tang >> >> Acked-by: Davidlohr Bueso >> >> ... but I believe you do have some left: >> >> drivers/scsi/scsi_lib.c: BUG_ON(unlikely(count > ivecs)); >> drivers/scsi/scsi_lib.c: BUG_ON(unlikely(count > queue_max_integrity_segments(rq->q))); >> kernel/sched/core.c: BUG_ON(unlikely(task_stack_end_corrupted(prev))); > >Thanks for your review, the left have been sended out already in two other patches. So given that the 'unlikely' is based on CONFIG_BUG/HAVE_ARCH_BUG_ON, the changelog needs to be rewritten. Ie mentioning at least why it should be ok to drop the redundant predictions: (1) For !CONFIG_BUG cases, the bug call is a no-op, so we couldn't care less and the change is ok. (2) ppc and mips, which HAVE_ARCH_BUG_ON, do not rely on branch predictions as it seems to be pointless[1] and thus callers should not be trying to push an optimization in the first place. Also, I think that all the changes should be in the same patch. Logically, this is a tree wide change, and trivial enough. But I don't really have a preference. Thanks, Davidlohr [1] http://lkml.iu.edu/hypermail/linux/kernel/1101.3/02289.html