From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>,
"Paul E. McKenney" <paulmck@kernel.org>,
linux-kernel@vger.kernel.org, Nicholas Piggin <npiggin@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Will Deacon <will@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Alan Stern <stern@rowland.harvard.edu>,
John Stultz <jstultz@google.com>,
Neeraj Upadhyay <Neeraj.Upadhyay@amd.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Frederic Weisbecker <frederic@kernel.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>,
Jonas Oberhauser <jonas.oberhauser@huaweicloud.com>,
rcu@vger.kernel.org, linux-mm@kvack.org, lkmm@lists.linux.dev
Subject: Re: [RFC PATCH v4 4/4] hazptr: Migrate per-CPU slots to backup slot on context switch
Date: Thu, 18 Dec 2025 19:21:28 -0500 [thread overview]
Message-ID: <bd86f598-97f9-4fc7-b426-01f08974b945@efficios.com> (raw)
In-Reply-To: <aUR9RfVChdcDncwX@tardis-2.local>
On 2025-12-18 17:16, Boqun Feng wrote:
[...]
>
> I would suggest we make CONFIG_PREEMPT_HAZPTR always enabled hence no
> need for a config, do we have the measurement of the additional cost?
Removing the PREEMPT_HAZPTR brings read-side performance
from 13.1 down to 5.1 ns. So there is a surprising amount
of work that goes into list_add/list_del.
I just noticed that I was running a kernel with CONFIG_LIST_HARDENED=y.
Reruning refscale for PREEMPT_HAZPTR=y with list hardening disabled
goes from 13.1 ns to 12.4ns, so not a huge win.
I did not notice much difference in terms of scheduler
performance with a quick hackbench run, but I cannot
claim it is an extensive benchmark in any way.
>
> I think you need to add interrupt disabling for chain/unchain because of
> the potential readers in interrupt and then you can avoid the preempt
> disabling in hazptr_release() I think. Let's aim for supporting readers
> in interrupt handler, because at least lockdep needs that.
OK, I'll look into it!
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
next prev parent reply other threads:[~2025-12-19 0:21 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-12-18 1:45 [RFC PATCH v4 0/4] Hazard Pointers Mathieu Desnoyers
2025-12-18 1:45 ` [RFC PATCH v4 1/4] compiler.h: Introduce ptr_eq() to preserve address dependency Mathieu Desnoyers
2025-12-18 9:03 ` David Laight
2025-12-18 13:51 ` Mathieu Desnoyers
2025-12-18 15:54 ` David Laight
2025-12-18 14:27 ` Gary Guo
2025-12-18 16:12 ` David Laight
2025-12-18 1:45 ` [RFC PATCH v4 2/4] Documentation: RCU: Refer to ptr_eq() Mathieu Desnoyers
2025-12-18 1:45 ` [RFC PATCH v4 3/4] hazptr: Implement Hazard Pointers Mathieu Desnoyers
2025-12-18 8:36 ` Boqun Feng
2025-12-18 17:35 ` Mathieu Desnoyers
2025-12-18 20:22 ` Boqun Feng
2025-12-18 23:36 ` Mathieu Desnoyers
2025-12-19 0:25 ` Boqun Feng
2025-12-19 6:06 ` Joel Fernandes
2025-12-19 15:14 ` Mathieu Desnoyers
2025-12-19 15:42 ` Joel Fernandes
2025-12-19 22:19 ` Mathieu Desnoyers
2025-12-19 22:39 ` Joel Fernandes
2025-12-21 9:59 ` Boqun Feng
2025-12-19 0:43 ` Boqun Feng
2025-12-19 14:22 ` Mathieu Desnoyers
2025-12-19 1:22 ` Joel Fernandes
2025-12-18 1:45 ` [RFC PATCH v4 4/4] hazptr: Migrate per-CPU slots to backup slot on context switch Mathieu Desnoyers
2025-12-18 16:20 ` Mathieu Desnoyers
2025-12-18 22:16 ` Boqun Feng
2025-12-19 0:21 ` Mathieu Desnoyers [this message]
2025-12-18 10:33 ` [RFC PATCH v4 0/4] Hazard Pointers Joel Fernandes
2025-12-18 17:54 ` Mathieu Desnoyers
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