From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id AFCC96B0388 for ; Wed, 1 Mar 2017 07:28:44 -0500 (EST) Received: by mail-pg0-f72.google.com with SMTP id d18so53421768pgh.2 for ; Wed, 01 Mar 2017 04:28:44 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id q6si4503249plk.257.2017.03.01.04.28.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Mar 2017 04:28:43 -0800 (PST) Date: Wed, 1 Mar 2017 13:28:43 +0100 From: Peter Zijlstra Subject: Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Message-ID: <20170301122843.GF6515@twins.programming.kicks-ass.net> References: <1484745459-2055-1-git-send-email-byungchul.park@lge.com> <1484745459-2055-7-git-send-email-byungchul.park@lge.com> <20170228134018.GK5680@worktop> <20170301054323.GE11663@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170301054323.GE11663@X58A-UD3R> Sender: owner-linux-mm@kvack.org List-ID: To: Byungchul Park 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, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, npiggin@gmail.com, kernel-team@lge.com On Wed, Mar 01, 2017 at 02:43:23PM +0900, Byungchul Park wrote: > On Tue, Feb 28, 2017 at 02:40:18PM +0100, Peter Zijlstra wrote: > > > +static int commit_xhlocks(struct cross_lock *xlock) > > > +{ > > > + struct task_struct *curr = current; > > > + struct hist_lock *xhlock_c = xhlock_curr(curr); > > > + struct hist_lock *xhlock = xhlock_c; > > > + > > > + do { > > > + xhlock = xhlock_prev(curr, xhlock); > > > + > > > + if (!xhlock_used(xhlock)) > > > + break; > > > + > > > + if (before(xhlock->hlock.gen_id, xlock->hlock.gen_id)) > > > + break; > > > + > > > + if (same_context_xhlock(xhlock) && > > > + before(xhlock->prev_gen_id, xlock->hlock.gen_id) && > > > + !commit_xhlock(xlock, xhlock)) > > > + return 0; > > > + } while (xhlock_c != xhlock); > > > + > > > + return 1; > > > +} > > > > So I'm still struggling with prev_gen_id; is it an optimization or is it > > required for correctness? > > It's an optimization, but very essential and important optimization. > > 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) > | E gen_id (1) prev_gen_id (NA) > > Let's consider the case that the gen id of xlock to commit is 3. > > In this case, it's engough to generate 'the xlock -> C'. 'the xlock -> B' > and 'the xlock -> A' are unnecessary since it's covered by 'C -> B' and > 'B -> A' which are already generated by original lockdep. > > I use the prev_gen_id to avoid adding this kind of redundant > dependencies. In other words, xhlock->prev_gen_id >= xlock->hlock.gen_id > means that the previous lock in hlocks[] is able to handle the > dependency on its commit stage. > Aah, I completely missed it was against held_locks. Hurm.. it feels like this is solving a problem we shouldn't be solving though. That is, ideally we'd already be able to (quickly) tell if a relation exists or not, but given how the whole chain_hash stuff is build now, it looks like we cannot. Let me think about this a bit more. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org