From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751534AbdGZHRK (ORCPT ); Wed, 26 Jul 2017 03:17:10 -0400 Received: from LGEAMRELO13.lge.com ([156.147.23.53]:55389 "EHLO lgeamrelo13.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750990AbdGZHRJ (ORCPT ); Wed, 26 Jul 2017 03:17:09 -0400 X-Original-SENDERIP: 156.147.1.127 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Wed, 26 Jul 2017 16:16:09 +0900 From: Byungchul Park To: Peter Zijlstra Cc: mingo@kernel.org, tglx@linutronix.de, walken@google.com, boqun.feng@gmail.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, willy@infradead.org, npiggin@gmail.com, kernel-team@lge.com Subject: Re: [PATCH v7 08/16] lockdep: Avoid adding redundant direct links of crosslocks Message-ID: <20170726071609.GN20323@X58A-UD3R> References: <1495616389-29772-1-git-send-email-byungchul.park@lge.com> <1495616389-29772-9-git-send-email-byungchul.park@lge.com> <20170725154136.hu3f2mjfunkyidnd@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170725154136.hu3f2mjfunkyidnd@hirez.programming.kicks-ass.net> 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 Tue, Jul 25, 2017 at 05:41:36PM +0200, Peter Zijlstra wrote: > On Wed, May 24, 2017 at 05:59:41PM +0900, Byungchul Park wrote: > > We can skip adding a dependency 'AX -> B', in case that we ensure 'AX -> > > the previous of B in hlocks' to be created, where AX is a crosslock and > > B is a typical lock. Remember that two adjacent locks in hlocks generate > > a dependency like 'prev -> next', that is, 'the previous of B in hlocks > > -> B' in this case. > > > > For example: > > > > in hlocks[] > > ------------ > > ^ A (gen_id: 4) --+ > > | | previous gen_id > > | B (gen_id: 3) <-+ > > | C (gen_id: 3) > > | D (gen_id: 2) > > oldest | E (gen_id: 1) > > > > in xhlocks[] > > ------------ > > ^ A (gen_id: 4, prev_gen_id: 3(B's gen id)) > > | B (gen_id: 3, prev_gen_id: 3(C's gen id)) > > | C (gen_id: 3, prev_gen_id: 2(D's gen id)) > > | D (gen_id: 2, prev_gen_id: 1(E's gen id)) > > oldest | E (gen_id: 1, prev_gen_id: NA) > > > > On commit for a crosslock AX(gen_id = 3), it's engough to add 'AX -> C', > > but adding 'AX -> B' and 'AX -> A' is unnecessary since 'AX -> C', 'C -> > > B' and 'B -> A' cover them, which are guaranteed to be generated. > > > > This patch intoduces a variable, prev_gen_id, to avoid adding this kind > > of redundant dependencies. In other words, the previous in hlocks will > > anyway handle it if the previous's gen_id >= the crosslock's gen_id. > > > > Didn't we talk about an alternative to this? Yes, we did. You said the optimazation was unnecessary, and I was not sure if it's true, so added it at this time. But *I will exclude this from next spin*. > > /me goes dig > > https://lkml.kernel.org/r/20170303091338.GH6536@twins.programming.kicks-ass.net > > There and replies. > > So how much does this save vs avoiding redundant links? No different on my qemu machine. The answer was: https://lkml.org/lkml/2017/3/14/103