From: Byungchul Park <byungchul.park@lge.com>
To: Peter Zijlstra <peterz@infradead.org>
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
Subject: Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature
Date: Wed, 1 Mar 2017 14:43:23 +0900 [thread overview]
Message-ID: <20170301054323.GE11663@X58A-UD3R> (raw)
In-Reply-To: <20170228134018.GK5680@worktop>
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.
next prev parent reply other threads:[~2017-03-01 5:44 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-18 13:17 [PATCH v5 00/13] lockdep: Implement crossrelease feature Byungchul Park
2017-01-18 13:17 ` [PATCH v5 01/13] lockdep: Refactor lookup_chain_cache() Byungchul Park
2017-01-19 9:16 ` Boqun Feng
2017-01-19 9:52 ` Byungchul Park
2017-01-26 7:53 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 02/13] lockdep: Fix wrong condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS Byungchul Park
2017-01-18 13:17 ` [PATCH v5 03/13] lockdep: Add a function building a chain between two classes Byungchul Park
2017-01-18 13:17 ` [PATCH v5 04/13] lockdep: Refactor save_trace() Byungchul Park
2017-01-18 13:17 ` [PATCH v5 05/13] lockdep: Pass a callback arg to check_prev_add() to handle stack_trace Byungchul Park
2017-01-26 7:43 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park
2017-02-28 12:26 ` Peter Zijlstra
2017-02-28 12:45 ` Peter Zijlstra
2017-02-28 12:49 ` Peter Zijlstra
2017-03-01 6:20 ` Byungchul Park
2017-02-28 13:05 ` Peter Zijlstra
2017-02-28 13:28 ` Byungchul Park
2017-02-28 13:35 ` Peter Zijlstra
2017-02-28 14:00 ` Byungchul Park
2017-02-28 13:10 ` Peter Zijlstra
2017-02-28 13:24 ` Byungchul Park
2017-02-28 18:29 ` Peter Zijlstra
2017-03-01 4:40 ` Byungchul Park
2017-03-01 10:45 ` Peter Zijlstra
2017-03-01 12:10 ` Byungchul Park
2017-02-28 13:40 ` Peter Zijlstra
2017-03-01 5:43 ` Byungchul Park [this message]
2017-03-01 12:28 ` Peter Zijlstra
2017-03-02 13:40 ` Peter Zijlstra
2017-03-03 0:17 ` Byungchul Park
2017-03-03 8:14 ` Peter Zijlstra
2017-03-03 9:13 ` Peter Zijlstra
2017-03-03 9:32 ` Peter Zijlstra
2017-03-05 3:33 ` Byungchul Park
2017-08-10 12:18 ` [tip:locking/core] locking/lockdep: Avoid creating redundant links tip-bot for Peter Zijlstra
2017-03-05 3:08 ` [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park
2017-03-07 11:42 ` Peter Zijlstra
2017-03-03 0:39 ` Byungchul Park
2017-02-28 15:49 ` Peter Zijlstra
2017-03-01 5:17 ` Byungchul Park
2017-03-01 6:18 ` Byungchul Park
2017-03-02 2:52 ` Byungchul Park
2017-02-28 18:15 ` Peter Zijlstra
2017-03-01 7:21 ` Byungchul Park
2017-03-01 10:43 ` Peter Zijlstra
2017-03-01 12:27 ` Byungchul Park
2017-03-02 4:20 ` Matthew Wilcox
2017-03-02 4:45 ` byungchul.park
2017-03-02 14:39 ` Matthew Wilcox
2017-03-02 23:50 ` Byungchul Park
2017-03-05 8:01 ` Byungchul Park
2017-03-14 7:36 ` Byungchul Park
2017-03-02 13:41 ` Peter Zijlstra
2017-03-02 23:43 ` Byungchul Park
2017-01-18 13:17 ` [PATCH v5 07/13] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park
2017-01-18 13:17 ` [PATCH v5 08/13] lockdep: Apply crossrelease to completions Byungchul Park
2017-01-18 13:17 ` [PATCH v5 09/13] pagemap.h: Remove trailing white space Byungchul Park
2017-01-18 13:17 ` [PATCH v5 10/13] lockdep: Apply crossrelease to PG_locked locks Byungchul Park
2017-01-18 13:17 ` [PATCH v5 11/13] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2017-01-18 13:17 ` [PATCH v5 12/13] lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2017-01-18 13:17 ` [PATCH v5 13/13] lockdep: Crossrelease feature documentation Byungchul Park
2017-01-20 9:08 ` [REVISED DOCUMENT] " Byungchul Park
2017-02-20 8:38 ` [PATCH v5 00/13] lockdep: Implement crossrelease feature Byungchul Park
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