From: Waiman Long <llong@redhat.com>
To: Yanfei Xu <yanfei.xu@windriver.com>,
peterz@infradead.org, mingo@redhat.com, will@kernel.org,
boqun.feng@gmail.com
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] locking/mutex: remove rcu_read_lock/unlock as we already disabled preemption
Date: Sun, 26 Sep 2021 15:16:48 -0400 [thread overview]
Message-ID: <9569eee4-266f-d83b-2af6-194a1a8b165c@redhat.com> (raw)
In-Reply-To: <20210926101624.2460704-1-yanfei.xu@windriver.com>
On 9/26/21 6:16 AM, Yanfei Xu wrote:
> preempt_disable/enable() is equal to RCU read-side crital section,
> and the mutex lock slowpath disable the preemption throughout the
> entire slowpath. Let's remove the rcu_read_lock/unlock for saving
> some cycles in hot codes.
The description is wrong. Preemption is disabled only in the optimistic
spinning code which is not the complete slowpath. Even though it may
sound reasonable that disable preemption is likely to prevent reaching
quiescent state, but I am not totally sure that will always be the case
as there are different RCU favors.
Cheers,
Longman
next prev parent reply other threads:[~2021-09-26 19:16 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-26 10:16 Yanfei Xu
2021-09-26 10:16 ` [PATCH 2/2] locking/rwsem: Use rcu_read_lock_sched to simplify codes Yanfei Xu
2021-09-26 19:22 ` Waiman Long
2021-09-27 16:41 ` Xu, Yanfei
2021-09-26 19:16 ` Waiman Long [this message]
2021-09-27 0:46 ` [PATCH 1/2] locking/mutex: remove rcu_read_lock/unlock as we already disabled preemption Waiman Long
2021-09-27 9:28 ` Xu, Yanfei
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