From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <Waiman.Long@hp.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
Scott J Norton <scott.norton@hp.com>,
Douglas Hatch <doug.hatch@hp.com>
Subject: Re: [PATCH 3/7] locking/pvqspinlock: Implement wait-early for overcommitted guest
Date: Sun, 12 Jul 2015 10:23:07 +0200 [thread overview]
Message-ID: <20150712082307.GT19282@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1436647018-49734-4-git-send-email-Waiman.Long@hp.com>
On Sat, Jul 11, 2015 at 04:36:54PM -0400, Waiman Long wrote:
> In an overcommitted guest where some vCPUs have to be halted to make
> forward progress in other areas, it is highly likely that a vCPU
> later in the spinlock queue will be spinning while the ones earlier in
> the queue would have been halted already. The spinning in the later
> vCPUs is then just a waste of precious CPU cycles because they are
> not going to get the lock soon as the earlier ones have to be woken
> up and take their turn to get the lock.
>
> This patch implements a wait-early mechanism where the vCPU will
> call pv_wait() earlier if the previous vCPU is in the halted state
> already. In this case, it will spin less before calling pv_wait(). On
> the other hand, if the previous vCPU was running and then becomes
> halted, the current vCPU will call pv_wait() immmediately in this case.
>
> This patch also separates the spin threshold for queue head and
> queue nodes. It favors the queue head by allowing it to spin longer
> before calling pv_wait().
-ENONUMBERS
next prev parent reply other threads:[~2015-07-12 8:23 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-11 20:36 [PATCH 0/7] locking/qspinlock: Enhance pvqspinlock & introduce queued unfair lock Waiman Long
2015-07-11 20:36 ` [PATCH 1/7] locking/pvqspinlock: Only kick CPU at unlock time Waiman Long
2015-07-13 12:02 ` Peter Zijlstra
2015-07-13 12:31 ` Peter Zijlstra
2015-07-15 1:24 ` Waiman Long
2015-07-13 13:48 ` Peter Zijlstra
2015-07-14 9:31 ` Peter Zijlstra
2015-07-15 1:31 ` Waiman Long
2015-08-03 17:00 ` [tip:locking/core] " tip-bot for Waiman Long
2015-07-11 20:36 ` [PATCH 2/7] locking/pvqspinlock: Allow vCPUs kick-ahead Waiman Long
2015-07-13 13:52 ` Peter Zijlstra
2015-07-15 1:38 ` Waiman Long
2015-07-11 20:36 ` [PATCH 3/7] locking/pvqspinlock: Implement wait-early for overcommitted guest Waiman Long
2015-07-12 8:23 ` Peter Zijlstra [this message]
2015-07-13 19:50 ` Davidlohr Bueso
2015-07-15 1:39 ` Waiman Long
2015-07-11 20:36 ` [PATCH 4/7] locking/pvqspinlock: Collect slowpath lock statistics Waiman Long
2015-07-12 8:22 ` Peter Zijlstra
2015-07-14 18:48 ` Waiman Long
2015-07-11 20:36 ` [PATCH 5/7] locking/pvqspinlock: Add pending bit support Waiman Long
2015-07-12 8:21 ` Peter Zijlstra
2015-07-14 18:47 ` Waiman Long
2015-07-11 20:36 ` [PATCH 6/7] locking/qspinlock: A fairer queued unfair lock Waiman Long
2015-07-12 8:21 ` Peter Zijlstra
2015-07-14 18:47 ` Waiman Long
2015-07-14 20:45 ` Peter Zijlstra
2015-07-11 20:36 ` [PATCH 7/7] locking/qspinlock: Collect queued unfair lock slowpath statistics Waiman Long
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