From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from Galois.linutronix.de ([146.0.238.70]:57234 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727760AbeLRWLd (ORCPT ); Tue, 18 Dec 2018 17:11:33 -0500 From: Sebastian Andrzej Siewior To: stable@vger.kernel.org Cc: Peter Zijlstra , Will Deacon , Thomas Gleixner , Daniel Wagner , bigeasy@linutronix.de, Waiman Long , Linus Torvalds , boqun.feng@gmail.com, linux-arm-kernel@lists.infradead.org, paulmck@linux.vnet.ibm.com, Ingo Molnar Subject: [PATCH STABLE v4.9 09/10] locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound Date: Tue, 18 Dec 2018 23:10:48 +0100 Message-Id: <20181218221049.6816-10-bigeasy@linutronix.de> In-Reply-To: <20181218221049.6816-1-bigeasy@linutronix.de> References: <20181218221049.6816-1-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: From: Will Deacon commit b247be3fe89b6aba928bf80f4453d1c4ba8d2063 upstream. On x86, atomic_cond_read_relaxed will busy-wait with a cpu_relax() loop, so it is desirable to increase the number of times we spin on the qspinlock lockword when it is found to be transitioning from pending to locked. According to Waiman Long: | Ideally, the spinning times should be at least a few times the typical | cacheline load time from memory which I think can be down to 100ns or | so for each cacheline load with the newest systems or up to several | hundreds ns for older systems. which in his benchmarking corresponded to 512 iterations. Suggested-by: Waiman Long Signed-off-by: Will Deacon Acked-by: Peter Zijlstra (Intel) Acked-by: Waiman Long Cc: Linus Torvalds Cc: Thomas Gleixner Cc: boqun.feng@gmail.com Cc: linux-arm-kernel@lists.infradead.org Cc: paulmck@linux.vnet.ibm.com Link: http://lkml.kernel.org/r/1524738868-31318-5-git-send-email-will.deacon@arm.com Signed-off-by: Ingo Molnar Signed-off-by: Sebastian Andrzej Siewior --- arch/x86/include/asm/qspinlock.h | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index e07cc206919d4..8b1ba1607091c 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -5,6 +5,8 @@ #include #include +#define _Q_PENDING_LOOPS (1 << 9) + #define queued_spin_unlock queued_spin_unlock /** * queued_spin_unlock - release a queued spinlock -- 2.20.1