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From: Byungchul Park <byungchul.park@lge.com>
To: Theodore Ts'o <tytso@mit.edu>
Cc: damien.lemoal@opensource.wdc.com, linux-ide@vger.kernel.org,
	adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org,
	torvalds@linux-foundation.org, mingo@redhat.com,
	linux-kernel@vger.kernel.org, peterz@infradead.org,
	will@kernel.org, tglx@linutronix.de, rostedt@goodmis.org,
	joel@joelfernandes.org, sashal@kernel.org,
	daniel.vetter@ffwll.ch, chris@chris-wilson.co.uk,
	duyuyang@gmail.com, johannes.berg@intel.com, tj@kernel.org,
	willy@infradead.org, david@fromorbit.com, amir73il@gmail.com,
	bfields@fieldses.org, gregkh@linuxfoundation.org,
	kernel-team@lge.com, linux-mm@kvack.org,
	akpm@linux-foundation.org, mhocko@kernel.org, minchan@kernel.org,
	hannes@cmpxchg.org, vdavydov.dev@gmail.com, sj@kernel.org,
	jglisse@redhat.com, dennis@kernel.org, cl@linux.com,
	penberg@kernel.org, rientjes@google.com, vbabka@suse.cz,
	ngupta@vflare.org, linux-block@vger.kernel.org,
	paolo.valente@linaro.org, josef@toxicpanda.com,
	linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	jack@suse.cz, jack@suse.com, jlayton@kernel.org,
	dan.j.williams@intel.com, hch@infradead.org, djwong@kernel.org,
	dri-devel@lists.freedesktop.org, airlied@linux.ie,
	rodrigosiqueiramelo@gmail.com, melissa.srw@gmail.com,
	hamohammed.sa@gmail.com
Subject: Re: Report 2 in ext4 and journal based on v5.17-rc1
Date: Fri, 4 Mar 2022 09:42:37 +0900	[thread overview]
Message-ID: <20220304004237.GB6112@X58A-UD3R> (raw)
In-Reply-To: <YiDSabde88HJ/aTt@mit.edu>

On Thu, Mar 03, 2022 at 09:36:25AM -0500, Theodore Ts'o wrote:
> On Thu, Mar 03, 2022 at 02:23:33PM +0900, Byungchul Park wrote:
> > I totally agree with you. *They aren't really locks but it's just waits
> > and wakeups.* That's exactly why I decided to develop Dept. Dept is not
> > interested in locks unlike Lockdep, but fouces on waits and wakeup
> > sources itself. I think you get Dept wrong a lot. Please ask me more if
> > you have things you doubt about Dept.
> 
> So the question is this --- do you now understand why, even though
> there is a circular dependency, nothing gets stalled in the
> interactions between the two wait channels?

??? I'm afraid I don't get you.

All contexts waiting for any of the events in the circular dependency
chain will be definitely stuck if there is a circular dependency as I
explained. So we need another wakeup source to break the circle. In
ext4 code, you might have the wakeup source for breaking the circle.

What I agreed with is:

   The case that 1) the circular dependency is unevitable 2) there are
   another wakeup source for breadking the circle and 3) the duration
   in sleep is short enough, should be acceptable.

Sounds good?

Thanks,
Byungchul

  reply	other threads:[~2022-03-04  0:43 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-02-17 10:57 [PATCH 00/16] DEPT(Dependency Tracker) Byungchul Park
2022-02-17 10:57 ` [PATCH 01/16] llist: Move llist_{head,node} definition to types.h Byungchul Park
2022-02-17 10:57 ` [PATCH 02/16] dept: Implement Dept(Dependency Tracker) Byungchul Park
2022-02-17 15:54   ` Steven Rostedt
2022-02-17 17:36   ` Steven Rostedt
2022-02-18  6:09     ` Byungchul Park
2022-02-17 19:46   ` kernel test robot
2022-02-17 19:46   ` kernel test robot
2022-02-17 10:57 ` [PATCH 03/16] dept: Embed Dept data in Lockdep Byungchul Park
2022-02-17 10:57 ` [PATCH 04/16] dept: Apply Dept to spinlock Byungchul Park
2022-02-17 10:57 ` [PATCH 05/16] dept: Apply Dept to mutex families Byungchul Park
2022-02-17 10:57 ` [PATCH 06/16] dept: Apply Dept to rwlock Byungchul Park
2022-02-17 10:57 ` [PATCH 07/16] dept: Apply Dept to wait_for_completion()/complete() Byungchul Park
2022-02-17 19:46   ` kernel test robot
2022-02-17 10:57 ` [PATCH 08/16] dept: Apply Dept to seqlock Byungchul Park
2022-02-17 10:57 ` [PATCH 09/16] dept: Apply Dept to rwsem Byungchul Park
2022-02-17 10:57 ` [PATCH 10/16] dept: Add proc knobs to show stats and dependency graph Byungchul Park
2022-02-17 15:55   ` Steven Rostedt
2022-02-17 10:57 ` [PATCH 11/16] dept: Introduce split map concept and new APIs for them Byungchul Park
2022-02-17 10:57 ` [PATCH 12/16] dept: Apply Dept to wait/event of PG_{locked,writeback} Byungchul Park
2022-02-17 10:57 ` [PATCH 13/16] dept: Apply SDT to swait Byungchul Park
2022-02-17 10:57 ` [PATCH 14/16] dept: Apply SDT to wait(waitqueue) Byungchul Park
2022-02-17 10:57 ` [PATCH 15/16] locking/lockdep, cpu/hotplus: Use a weaker annotation in AP thread Byungchul Park
2022-02-17 10:57 ` [PATCH 16/16] dept: Distinguish each syscall context from another Byungchul Park
2022-02-17 11:10 ` Report 1 in ext4 and journal based on v5.17-rc1 Byungchul Park
2022-02-17 11:10   ` Report 2 " Byungchul Park
2022-02-21 19:02     ` Jan Kara
2022-02-23  0:35       ` Byungchul Park
2022-02-23 14:48         ` Jan Kara
2022-02-24  1:11           ` Byungchul Park
2022-02-24 10:22             ` Jan Kara
2022-02-28  9:28               ` Byungchul Park
2022-02-28 10:14                 ` Jan Kara
2022-02-28 21:25                   ` Theodore Ts'o
2022-03-03  1:36                     ` Byungchul Park
2022-03-03  1:00                   ` Byungchul Park
2022-03-03  2:32                     ` Theodore Ts'o
2022-03-03  5:23                       ` Byungchul Park
2022-03-03 14:36                         ` Theodore Ts'o
2022-03-04  0:42                           ` Byungchul Park [this message]
2022-03-05  3:26                             ` Theodore Ts'o
2022-03-05 14:15                               ` Byungchul Park
2022-03-05 15:05                                 ` Joel Fernandes
2022-03-07  2:43                                   ` Byungchul Park
2022-03-04  3:20                           ` Byungchul Park
2022-03-05  3:40                             ` Theodore Ts'o
2022-03-05 14:55                               ` Byungchul Park
2022-03-05 15:12                                 ` Reimar Döffinger
2022-03-06  3:30                                 ` Theodore Ts'o
2022-03-06 10:51                                   ` Byungchul Park
2022-03-06 14:19                                     ` Theodore Ts'o
2022-03-10  1:45                                       ` Byungchul Park
2022-03-03  9:54                     ` Jan Kara
2022-03-04  1:56                       ` Byungchul Park
2022-02-17 13:27   ` Report 1 " Matthew Wilcox
2022-02-18  0:41     ` Byungchul Park
2022-02-22  8:27   ` Jan Kara
2022-02-23  1:40     ` Byungchul Park
2022-02-23  3:30     ` Byungchul Park
2022-02-17 15:51 ` [PATCH 00/16] DEPT(Dependency Tracker) Theodore Ts'o
2022-02-17 17:00   ` Steven Rostedt
2022-02-17 17:06     ` Matthew Wilcox
2022-02-19 10:05       ` Byungchul Park
2022-02-18  4:19     ` Theodore Ts'o
2022-02-19 10:34       ` Byungchul Park
2022-02-19 10:18     ` Byungchul Park
2022-02-19  9:54   ` Byungchul Park

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