From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
huang ying <huang.ying.caritas@gmail.com>
Subject: Re: [PATCH-tip v3 05/14] locking/rwsem: Remove rwsem_wake() wakeup optimization
Date: Thu, 11 Apr 2019 09:25:29 +0200 [thread overview]
Message-ID: <20190411072529.GA4038@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190410184231.6748-6-longman@redhat.com>
On Wed, Apr 10, 2019 at 02:42:22PM -0400, Waiman Long wrote:
> With the commit 59aabfc7e959 ("locking/rwsem: Reduce spinlock contention
> in wakeup after up_read()/up_write()"), the rwsem_wake() forgoes doing
> a wakeup if the wait_lock cannot be directly acquired and an optimistic
> spinning locker is present. This can help performance by avoiding
> spinning on the wait_lock when it is contended.
>
> With the later commit 133e89ef5ef3 ("locking/rwsem: Enable lockless
> waiter wakeup(s)"), the performance advantage of the above optimization
> diminishes as the average wait_lock hold time become much shorter.
>
> By supporting rwsem lock handoff, we can no longer relies on the fact
> that the presence of an optimistic spinning locker will ensure that the
> lock will be acquired by a task soon. This can lead to missed wakeup
> and application hang. So the commit 59aabfc7e959 ("locking/rwsem:
> Reduce spinlock contention in wakeup after up_read()/up_write()")
> will have to be reverted.
Does it make sense to make this patch #3 in this series? The less code
there is, the easier to review the other patches.
next prev parent reply other threads:[~2019-04-11 7:25 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-10 18:42 [PATCH-tip v3 00/14] locking/rwsem: Rwsem rearchitecture part 2 Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 01/14] locking/rwsem: Prevent unneeded warning during locking selftest Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 02/14] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER Waiman Long
2019-04-11 8:12 ` Peter Zijlstra
2019-04-11 16:03 ` Waiman Long
2019-04-12 7:02 ` Ingo Molnar
2019-04-12 7:05 ` Peter Zijlstra
2019-04-12 7:09 ` Ingo Molnar
2019-04-12 14:04 ` Waiman Long
2019-04-12 14:07 ` Waiman Long
2019-04-12 14:22 ` Waiman Long
2019-04-12 16:41 ` Ingo Molnar
2019-04-12 18:05 ` Waiman Long
2019-04-13 2:24 ` Waiman Long
2019-04-15 13:43 ` Waiman Long
2019-04-16 7:53 ` Ingo Molnar
2019-04-12 18:21 ` Peter Zijlstra
2019-04-10 18:42 ` [PATCH-tip v3 03/14] locking/rwsem: Implement a new locking scheme Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 04/14] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-04-10 19:38 ` Peter Zijlstra
2019-04-10 20:28 ` Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 05/14] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-04-11 7:25 ` Peter Zijlstra [this message]
2019-04-11 15:55 ` Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 06/14] locking/rwsem: Make rwsem_spin_on_owner() return owner state Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 07/14] locking/rwsem: Ensure an RT task will not spin on reader Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 08/14] locking/rwsem: Wake up almost all readers in wait queue Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 09/14] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 10/14] locking/rwsem: Enable time-based spinning on reader-owned rwsem Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 11/14] locking/rwsem: Add more rwsem owner access helpers Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 12/14] locking/rwsem: Guard against making count negative Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 13/14] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-04-10 18:42 ` [PATCH-tip v3 14/14] locking/rwsem: Remove redundant computation of writer lock word Waiman Long
2019-04-11 8:37 ` [PATCH-tip v3 00/14] locking/rwsem: Rwsem rearchitecture part 2 Peter Zijlstra
2019-04-11 16:09 ` Waiman Long
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