From: Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>
Cc: linux-kernel@vger.kernel.org, Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Alan Stern <stern@rowland.harvard.edu>,
John Stultz <jstultz@google.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Frederic Weisbecker <frederic@kernel.org>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Uladzislau Rezki <urezki@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
Ingo Molnar <mingo@redhat.com>, Waiman Long <longman@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Vlastimil Babka <vbabka@suse.cz>,
maged.michael@gmail.com, Mateusz Guzik <mjguzik@gmail.com>,
rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev
Subject: Re: [RFC PATCH 1/1] hpref: Hazard Pointers with Reference Counter
Date: Sat, 28 Sep 2024 13:22:18 +0200 [thread overview]
Message-ID: <db17633f-354d-428e-97c2-bcd455766c3a@huaweicloud.com> (raw)
In-Reply-To: <20240921164210.256278-1-mathieu.desnoyers@efficios.com>
Two more questions below:
Am 9/21/2024 um 6:42 PM schrieb Mathieu Desnoyers:
> +#define NR_PERCPU_SLOTS_BITS 3
Have you measured any advantage of this multi-slot version vs a version
with just one normal slot and one emergency slot?
With just one normal slot, the normal slot version would always be zero,
and there'd be no need to increment etc., which might make the common
case (no conflict) faster.
Either way I recommend stress testing with just one normal slot to
increase the chance of conflict (and hence triggering corner cases)
during stress testing.
> +retry:
> + node = uatomic_load(node_p, CMM_RELAXED);
> + if (!node)
> + return false;
> + /* Use rseq to try setting current slot hp. Store B. */
> + if (rseq_load_cbne_store__ptr(RSEQ_MO_RELAXED, RSEQ_PERCPU_CPU_ID,
> + (intptr_t *) &slot->node, (intptr_t) NULL,
> + (intptr_t) node, cpu)) {
> + slot = &cpu_slots->slots[HPREF_EMERGENCY_SLOT];
> + use_refcount = true;
> + /*
> + * This may busy-wait for another reader using the
> + * emergency slot to transition to refcount.
> + */
> + caa_cpu_relax();
> + goto retry;
> + }
I'm not familiar with Linux' preemption model. Can this deadlock if a
low-interrupt-level thread is occupying the EMERGENCY slot and a
higher-interrupt-level thread is also trying to take it?
Best wishes,
jonas
next prev parent reply other threads:[~2024-09-28 11:22 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-21 16:42 [RFC PATCH 1/1] hpref: Hazard Pointers with Reference Counter Mathieu Desnoyers
2024-09-21 21:07 ` Lai Jiangshan
2024-09-22 7:47 ` Mathieu Desnoyers
2024-09-25 5:57 ` Jonas Oberhauser
2024-09-25 6:35 ` Mathieu Desnoyers
2024-09-25 10:06 ` Jonas Oberhauser
2024-09-25 11:36 ` Mathieu Desnoyers
2024-09-25 12:02 ` Jonas Oberhauser
2024-09-28 11:22 ` Jonas Oberhauser [this message]
2024-09-28 11:33 ` Mathieu Desnoyers
2024-09-28 11:50 ` Jonas Oberhauser
2024-09-30 13:31 ` Jonas Oberhauser
2024-10-01 15:24 ` Paul E. McKenney
2026-01-06 14:52 ` Mathieu Desnoyers
2026-01-07 9:38 ` Jonas Oberhauser
2026-01-07 14:40 ` Mathieu Desnoyers
2026-01-07 17:48 ` Paul E. McKenney
2026-01-07 20:04 ` Mathieu Desnoyers
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