From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: kernel test robot <oliver.sang@intel.com>,
oe-lkp@lists.linux.dev, lkp@intel.com,
linux-kernel@vger.kernel.org, rcu@vger.kernel.org
Subject: Re: [linus:master] [rcu/nocb] 7625926086: WARNING:at_kernel/rcu/tree_nocb.h:#rcu_nocb_try_bypass
Date: Wed, 12 Jul 2023 18:59:38 +0200 [thread overview]
Message-ID: <ZK7b+vIJpOZhndbm@lothringen> (raw)
In-Reply-To: <842683bc-5859-48be-8ca5-17a1e4bf3f39@paulmck-laptop>
On Tue, Jul 11, 2023 at 09:41:58AM -0700, Paul E. McKenney wrote:
> On Tue, Jul 11, 2023 at 06:06:11PM +0200, Frederic Weisbecker wrote:
> Heh!
>
> The purpose was to see if this lock was ever contended. I guess we now
> have an answer, which is "Yes, but rarely."
>
> It looks like the victim commit increased the size of the ->nocb_lock
> critical section, just enough to make this happen sometimes.
>
> Removing the WARN_ON_ONCE() seems appropriate, especially given that
> this only happens when shrinking.
Ok, I'll check that.
> Should we add something that monitors that lock's contention? It is
> often the case that lock contention rises over time as new features and
> optimizations are added.
I'm not sure. Should we keep the current ->nocb_lock_contended based engine
to report contention somehow somewhere? Also does it behave better than our
current spinlock slow path implementations?
Thanks.
next prev parent reply other threads:[~2023-07-12 16:59 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-11 8:48 [linus:master] [rcu/nocb] 7625926086: WARNING:at_kernel/rcu/tree_nocb.h:#rcu_nocb_try_bypass kernel test robot
2023-07-11 9:45 ` Z qiang
2023-07-11 10:04 ` Z qiang
2023-07-11 16:06 ` Frederic Weisbecker
2023-07-11 16:41 ` Paul E. McKenney
2023-07-12 16:59 ` Frederic Weisbecker [this message]
2023-07-12 20:48 ` Paul E. McKenney
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