From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Sasha Levin <sashal@kernel.org>,
"Peter Zijlstra \(Intel\)" <peterz@infradead.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
boqun.feng@gmail.com, Will Deacon <will.deacon@arm.com>,
stable@vger.kernel.org,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Waiman Long <longman@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
paulmck@linux.vnet.ibm.com,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: [PATCH 4.9 28/61] locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound
Date: Thu, 20 Dec 2018 10:18:28 +0100 [thread overview]
Message-ID: <20181220085844.858853635@linuxfoundation.org> (raw)
In-Reply-To: <20181220085843.743900603@linuxfoundation.org>
4.9-stable review patch. If anyone has any objections, please let me know.
------------------
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 <longman@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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 <mingo@kernel.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 e07cc206919d..8b1ba1607091 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -5,6 +5,8 @@
#include <asm-generic/qspinlock_types.h>
#include <asm/paravirt.h>
+#define _Q_PENDING_LOOPS (1 << 9)
+
#define queued_spin_unlock queued_spin_unlock
/**
* queued_spin_unlock - release a queued spinlock
--
2.19.1
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next prev parent reply other threads:[~2018-12-20 9:23 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20181220085843.743900603@linuxfoundation.org>
2018-12-20 9:18 ` [PATCH 4.9 22/61] locking/qspinlock: Bound spinning on pending->locked transition in slowpath Greg Kroah-Hartman
2018-12-20 9:18 ` [PATCH 4.9 23/61] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Greg Kroah-Hartman
2018-12-20 9:18 ` [PATCH 4.9 24/61] locking/qspinlock: Remove unbounded cmpxchg() loop from locking slowpath Greg Kroah-Hartman
2018-12-20 9:18 ` [PATCH 4.9 25/61] locking/qspinlock: Remove duplicate clear_pending() function from PV code Greg Kroah-Hartman
2018-12-20 9:18 ` [PATCH 4.9 26/61] locking/qspinlock: Kill cmpxchg() loop when claiming lock from head of queue Greg Kroah-Hartman
2018-12-20 9:18 ` Greg Kroah-Hartman [this message]
2018-12-20 9:18 ` [PATCH 4.9 30/61] locking/qspinlock: Fix build for anonymous union in older GCC compilers Greg Kroah-Hartman
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