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,
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
Date: Wed, 26 Jul 2017 16:16:09 +0900 [thread overview]
Message-ID: <20170726071609.GN20323@X58A-UD3R> (raw)
In-Reply-To: <20170725154136.hu3f2mjfunkyidnd@hirez.programming.kicks-ass.net>
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
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next prev parent reply other threads:[~2017-07-26 7:17 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 8:59 [PATCH v7 00/16] lockdep: Implement crossrelease feature Byungchul Park
2017-05-24 8:59 ` [PATCH v7 01/16] lockdep: Refactor lookup_chain_cache() Byungchul Park
2017-05-24 8:59 ` [PATCH v7 02/16] lockdep: Add a function building a chain between two classes Byungchul Park
2017-05-24 8:59 ` [PATCH v7 03/16] lockdep: Change the meaning of check_prev_add()'s return value Byungchul Park
2017-05-24 8:59 ` [PATCH v7 04/16] lockdep: Make check_prev_add() able to handle external stack_trace Byungchul Park
2017-05-24 8:59 ` [PATCH v7 05/16] lockdep: Implement crossrelease feature Byungchul Park
2017-06-13 0:33 ` Byungchul Park
2017-06-22 23:27 ` Byungchul Park
2017-07-11 16:04 ` Peter Zijlstra
2017-07-12 2:24 ` Byungchul Park
2017-05-24 8:59 ` [PATCH v7 06/16] lockdep: Detect and handle hist_lock ring buffer overwrite Byungchul Park
2017-07-11 16:12 ` Peter Zijlstra
2017-07-12 2:00 ` Byungchul Park
2017-07-12 7:56 ` Peter Zijlstra
2017-07-13 2:07 ` Byungchul Park
2017-07-13 8:14 ` Peter Zijlstra
2017-07-13 8:57 ` Byungchul Park
2017-07-13 9:50 ` Peter Zijlstra
2017-07-13 10:09 ` Byungchul Park
2017-07-13 10:29 ` Peter Zijlstra
2017-07-13 11:12 ` Peter Zijlstra
2017-07-13 11:23 ` Byungchul Park
2017-07-14 1:41 ` Byungchul Park
2017-07-14 6:42 ` Byungchul Park
2017-07-21 13:54 ` Peter Zijlstra
2017-07-25 6:29 ` Byungchul Park
2017-07-25 8:45 ` Peter Zijlstra
2017-07-13 11:19 ` Byungchul Park
2017-07-18 1:25 ` Byungchul Park
2017-05-24 8:59 ` [PATCH v7 07/16] lockdep: Handle non(or multi)-acquisition of a crosslock Byungchul Park
2017-05-24 8:59 ` [PATCH v7 08/16] lockdep: Avoid adding redundant direct links of crosslocks Byungchul Park
2017-07-25 15:41 ` Peter Zijlstra
2017-07-26 7:16 ` Byungchul Park [this message]
2017-05-24 8:59 ` [PATCH v7 09/16] lockdep: Fix incorrect condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS Byungchul Park
2017-05-24 8:59 ` [PATCH v7 10/16] lockdep: Make print_circular_bug() aware of crossrelease Byungchul Park
2017-05-24 8:59 ` [PATCH v7 11/16] lockdep: Apply crossrelease to completions Byungchul Park
2017-05-24 8:59 ` [PATCH v7 12/16] pagemap.h: Remove trailing white space Byungchul Park
2017-05-24 8:59 ` [PATCH v7 13/16] lockdep: Apply crossrelease to PG_locked locks Byungchul Park
2017-05-24 8:59 ` [PATCH v7 14/16] lockdep: Apply lock_acquire(release) on __Set(__Clear)PageLocked Byungchul Park
2017-05-24 8:59 ` [PATCH v7 15/16] lockdep: Move data of CONFIG_LOCKDEP_PAGELOCK from page to page_ext Byungchul Park
2017-05-24 8:59 ` [PATCH v7 16/16] lockdep: Crossrelease feature documentation Byungchul Park
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