From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Peter Zijlstra <peterz@infradead.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
syzkaller <syzkaller@googlegroups.com>,
Dmitry Vyukov <dvyukov@google.com>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Boqun Feng <boqun.feng@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
USB list <linux-usb@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Hillf Danton <hdanton@sina.com>
Subject: Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate_class() with unique class keys
Date: Mon, 13 Feb 2023 18:51:57 +0100 [thread overview]
Message-ID: <Y+p4vUqOE87WGwuD@kroah.com> (raw)
In-Reply-To: <Y+pi6pA0d22g7sCE@rowland.harvard.edu>
On Mon, Feb 13, 2023 at 11:18:50AM -0500, Alan Stern wrote:
> On Mon, Feb 13, 2023 at 10:49:50AM +0100, Peter Zijlstra wrote:
> > My main worry when adding a ton of classes like this is the
> > combinatorics (dynamic classes make this more trivial, but it's entirely
> > possible with just static classes too).
> >
> > As an example, we used to have a static class per cpu runqueue, now,
> > given migration takes two runqueue locks (per locking rules in cpu
> > order -- source and dest runqueue etc..) we got O(n^2) combinations of
> > class orderings, which lead to a giant graph, which led to both
> > performance and memory usage issues.
>
> Having a new class for each device would add a lot of classes. Just how
> badly this would affect lockdep's performance is hard to predict.
> Testing seems like the best way to find out.
We support systems with 50000+ devices today, so one class per device
might be messy.
But back to the original issue here, why any of this? What's wrong with
what we have now? I haven't seen real locking issues reported yet (only
odd syzbot reports that didn't make any sense.) Is this effort even
worth it?
thanks,
greg k-h
next prev parent reply other threads:[~2023-02-13 17:52 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-04 13:32 Converting dev->mutex into dev->spinlock ? Tetsuo Handa
2023-02-04 13:47 ` Greg Kroah-Hartman
2023-02-04 14:21 ` Tetsuo Handa
2023-02-04 14:34 ` Greg Kroah-Hartman
2023-02-04 15:16 ` Tetsuo Handa
2023-02-04 15:34 ` Alan Stern
2023-02-04 16:12 ` Tetsuo Handa
2023-02-04 16:27 ` Alan Stern
2023-02-04 17:09 ` Tetsuo Handa
2023-02-04 20:01 ` Alan Stern
2023-02-04 20:14 ` Linus Torvalds
2023-02-05 1:23 ` Alan Stern
2023-02-06 14:13 ` Tetsuo Handa
2023-02-06 15:45 ` Alan Stern
2023-02-07 13:07 ` Tetsuo Handa
2023-02-07 17:46 ` Alan Stern
2023-02-07 22:17 ` Tetsuo Handa
2023-02-08 0:34 ` Alan Stern
[not found] ` <20230208080739.1649-1-hdanton@sina.com>
2023-02-08 10:30 ` [PATCH] drivers/core: Replace lockdep_set_novalidate_class() with unique class keys Tetsuo Handa
2023-02-08 15:07 ` Alan Stern
2023-02-09 0:22 ` Tetsuo Handa
2023-02-09 0:46 ` Linus Torvalds
2023-02-09 1:50 ` Tetsuo Handa
2023-02-09 2:26 ` Alan Stern
2023-02-11 2:04 ` Tetsuo Handa
2023-02-11 21:41 ` [PATCH RFC] " Alan Stern
2023-02-11 21:51 ` Linus Torvalds
2023-02-11 23:06 ` Kent Overstreet
2023-02-11 23:08 ` Kent Overstreet
2023-02-11 23:24 ` Kent Overstreet
2023-02-12 2:40 ` Alan Stern
2023-02-12 2:46 ` Kent Overstreet
2023-02-12 3:03 ` Alan Stern
2023-02-12 3:10 ` Kent Overstreet
2023-02-12 15:23 ` Alan Stern
2023-02-12 19:14 ` Kent Overstreet
2023-02-12 20:19 ` Alan Stern
2023-02-12 20:51 ` Kent Overstreet
2023-02-13 1:23 ` Alan Stern
2023-02-13 2:21 ` Kent Overstreet
2023-02-13 15:25 ` Alan Stern
2023-02-13 9:29 ` Peter Zijlstra
2023-02-13 9:27 ` Peter Zijlstra
2023-02-13 15:28 ` Alan Stern
2023-02-13 16:36 ` Peter Zijlstra
2023-02-13 9:24 ` Peter Zijlstra
2023-02-13 15:25 ` Alan Stern
2023-02-13 16:29 ` Peter Zijlstra
2023-02-14 1:51 ` Boqun Feng
2023-02-14 1:53 ` Boqun Feng
2023-02-14 2:03 ` Alan Stern
2023-02-14 2:09 ` Boqun Feng
[not found] ` <20230214052733.3354-1-hdanton@sina.com>
2023-02-14 5:55 ` Boqun Feng
2023-02-14 10:48 ` Peter Zijlstra
2023-02-14 16:22 ` Boqun Feng
2023-02-15 10:45 ` Peter Zijlstra
2023-02-20 17:32 ` Boqun Feng
2023-02-13 18:46 ` Kent Overstreet
2023-02-14 11:05 ` Peter Zijlstra
2023-02-14 20:05 ` Alan Stern
2023-02-15 10:33 ` Peter Zijlstra
2023-02-14 20:16 ` Kent Overstreet
[not found] ` <20230212013220.2678-1-hdanton@sina.com>
2023-02-12 1:52 ` Kent Overstreet
2023-02-13 9:49 ` Peter Zijlstra
2023-02-13 16:18 ` Alan Stern
2023-02-13 17:51 ` Greg Kroah-Hartman [this message]
2023-02-13 18:05 ` Alan Stern
2023-02-05 1:31 ` Converting dev->mutex into dev->spinlock ? Tetsuo Handa
2023-02-05 16:46 ` Alan Stern
2023-02-06 2:56 ` Hillf Danton
2023-02-06 4:44 ` Matthew Wilcox
2023-02-06 5:17 ` Greg Kroah-Hartman
2023-02-06 6:43 ` Hillf Danton
2023-02-06 6:48 ` Greg Kroah-Hartman
2023-02-04 15:12 ` Alan Stern
2023-02-04 15:30 ` Tetsuo Handa
2023-02-04 15:40 ` Alan Stern
2023-02-05 0:21 ` Hillf Danton
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