From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH v2 2/6] locking/lockdep: Throw away all lock chains with zapped class
Date: Mon, 13 Jan 2020 10:44:37 -0500 [thread overview]
Message-ID: <2c742217-fa18-bf87-2c0d-2c7f95887646@redhat.com> (raw)
In-Reply-To: <20200113151806.GW2844@hirez.programming.kicks-ass.net>
On 1/13/20 10:18 AM, Peter Zijlstra wrote:
> On Mon, Dec 16, 2019 at 10:15:13AM -0500, Waiman Long wrote:
>> If a lock chain contains a class that is zapped, the whole lock chain is
>> now invalid.
> Possibly. But I'm thinking that argument can/should be made mode elaborate.
>
> Suppose we have A->B->C, and we're about to remove B.
>
> Now, I suppose the trivial argument goes that if we remove the text that
> causes A->B, then so B->C will no longer happen. However, that doesn't
> mean A->C won't still occur.
>
> OTOH, we might already have A->C and so our resulting chain would be a
> duplicate. Conversely, if we didn't already have A->C and it does indeed
> still occur (say it was omitted due to the redundant logic), then we
> will create this dependency the next time we'll encounter it.
I will prefer having it only when it actually happens rather than
leaving a partial chain behind assuming that it may happen.
>
> Bart, do you see a problem with this reasoning?
>
> In short, yes, I think you're right and we can remove the whole thing.
> But please, expand the Changelog a bit, possibly add some of this
> reasoning into a comment.
>
Yes, I will elaborate more in the changelog.
Cheers,
Longman
next prev parent reply other threads:[~2020-01-13 15:44 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 15:15 [PATCH v2 0/6] locking/lockdep: Reuse zapped chain_hlocks entries Waiman Long
2019-12-16 15:15 ` [PATCH v2 1/6] locking/lockdep: Track number of zapped classes Waiman Long
2020-01-13 14:55 ` Peter Zijlstra
2020-01-13 14:58 ` Waiman Long
2020-01-13 16:02 ` Bart Van Assche
2019-12-16 15:15 ` [PATCH v2 2/6] locking/lockdep: Throw away all lock chains with zapped class Waiman Long
2020-01-13 15:18 ` Peter Zijlstra
2020-01-13 15:44 ` Waiman Long [this message]
2020-01-13 16:05 ` Bart Van Assche
2020-01-13 16:15 ` Waiman Long
2019-12-16 15:15 ` [PATCH v2 3/6] locking/lockdep: Track number of zapped lock chains Waiman Long
2019-12-16 15:15 ` [PATCH v2 4/6] locking/lockdep: Reuse freed chain_hlocks entries Waiman Long
2020-01-13 15:51 ` Peter Zijlstra
2020-01-13 16:04 ` Waiman Long
2020-01-13 15:58 ` Peter Zijlstra
2020-01-13 16:24 ` Waiman Long
2020-01-14 9:46 ` Peter Zijlstra
2020-01-14 19:16 ` Waiman Long
2020-01-15 10:44 ` Peter Zijlstra
2020-01-15 19:26 ` Waiman Long
2020-01-13 15:59 ` Peter Zijlstra
2020-01-13 16:03 ` Waiman Long
2019-12-16 15:15 ` [PATCH v2 5/6] locking/lockdep: Decrement irq context counters when removing lock chain Waiman Long
2020-01-14 9:53 ` Peter Zijlstra
2020-01-14 15:04 ` Waiman Long
2019-12-16 15:15 ` [PATCH v2 6/6] locking/lockdep: Display irq_context names in /proc/lockdep_chains Waiman Long
2020-01-06 15:54 ` [PATCH v2 0/6] locking/lockdep: Reuse zapped chain_hlocks entries Waiman Long
2020-01-06 16:50 ` Peter Zijlstra
2020-01-06 16:52 ` Waiman Long
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