From: Peter Zijlstra <peterz@infradead.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Waiman Long <llong@redhat.com>,
linux-kernel@vger.kernel.org,
Andr?? Almeida <andrealmeid@igalia.com>,
Darren Hart <dvhart@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
Valentin Schneider <vschneid@redhat.com>
Subject: Re: [PATCH 2/3] futex: Use RCU-based per-CPU reference counting instead of rcuref_t
Date: Tue, 8 Jul 2025 21:06:05 +0200 [thread overview]
Message-ID: <20250708190605.GF477119@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20250708134708.Rgh8nHcx@linutronix.de>
On Tue, Jul 08, 2025 at 03:47:08PM +0200, Sebastian Andrzej Siewior wrote:
> On 2025-07-08 09:43:44 [-0400], Waiman Long wrote:
> > This looks somewhat like what the percpu refcount does (see
> > lib/percpu-refcount.c). Could this be used instead of reinventing the wheel
> > again?
>
> From the comment:
>
> * futex-ref
> *
> * Heavily inspired by percpu-rwsem/percpu-refcount; not reusing any of that
> * code because it just doesn't fit right.
> *
> * Dual counter, per-cpu / atomic approach like percpu-refcount, except it
> * re-initializes the state automatically, such that the fph swizzle is also a
> * transition back to per-cpu.
>
> but I leave it up to Peter if he considers merging that.
Basically what the comment says. Trying to reuse things ended up in a
mess. It really isn't much code, most of it is comments.
next prev parent reply other threads:[~2025-07-08 19:06 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-07 14:36 [PATCH 0/3] futex: Use RCU-based per-CPU reference counting Sebastian Andrzej Siewior
2025-07-07 14:36 ` [PATCH 1/3] selftests/futex: Adapt the private hash test to RCU related changes Sebastian Andrzej Siewior
2025-07-08 7:41 ` Peter Zijlstra
2025-07-08 8:01 ` Sebastian Andrzej Siewior
2025-07-10 8:08 ` Sebastian Andrzej Siewior
2025-07-07 14:36 ` [PATCH 2/3] futex: Use RCU-based per-CPU reference counting instead of rcuref_t Sebastian Andrzej Siewior
2025-07-08 6:51 ` Sebastian Andrzej Siewior
2025-07-08 8:56 ` Hillf Danton
2025-07-08 9:16 ` Sebastian Andrzej Siewior
2025-07-08 12:01 ` Hillf Danton
2025-07-08 13:15 ` Sebastian Andrzej Siewior
2025-07-08 22:00 ` Hillf Danton
2025-07-08 13:09 ` Sebastian Andrzej Siewior
2025-07-08 13:43 ` Waiman Long
2025-07-08 13:47 ` Sebastian Andrzej Siewior
2025-07-08 19:06 ` Peter Zijlstra [this message]
2025-07-10 15:58 ` Waiman Long
2025-07-07 14:36 ` [PATCH 3/3] futex: Make futex_private_hash_get() static Sebastian Andrzej Siewior
2025-07-08 7:50 ` [PATCH 0/3] futex: Use RCU-based per-CPU reference counting Peter Zijlstra
2025-07-08 8:02 ` Sebastian Andrzej Siewior
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