From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:38971 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753140AbbJMUq3 (ORCPT ); Tue, 13 Oct 2015 16:46:29 -0400 Subject: Patch "locking/qspinlock/x86: Fix performance regression under unaccelerated VMs" has been added to the 4.2-stable tree To: peterz@infradead.org, Waiman.Long@hp.com, david@fromorbit.com, gregkh@linuxfoundation.org, mingo@kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org Cc: , From: Date: Tue, 13 Oct 2015 13:39:54 -0700 Message-ID: <1444768794125129@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled locking/qspinlock/x86: Fix performance regression under unaccelerated VMs to the 4.2-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: locking-qspinlock-x86-fix-performance-regression-under-unaccelerated-vms.patch and it can be found in the queue-4.2 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 43b3f02899f74ae9914a39547cc5492156f0027a Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 4 Sep 2015 17:25:23 +0200 Subject: locking/qspinlock/x86: Fix performance regression under unaccelerated VMs From: Peter Zijlstra commit 43b3f02899f74ae9914a39547cc5492156f0027a upstream. Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS set and Linus noted that the test-and-set implementation was retarded. One should spin on the variable with a load, not a RMW. While there, remove 'queued' from the name, as the lock isn't queued at all, but a simple test-and-set. Suggested-by: Linus Torvalds Reported-by: Dave Chinner Tested-by: Dave Chinner Signed-off-by: Peter Zijlstra (Intel) Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Waiman Long Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h index 9d51fae1cba3..8dde3bdc4a05 100644 --- a/arch/x86/include/asm/qspinlock.h +++ b/arch/x86/include/asm/qspinlock.h @@ -39,15 +39,23 @@ static inline void queued_spin_unlock(struct qspinlock *lock) } #endif -#define virt_queued_spin_lock virt_queued_spin_lock +#define virt_spin_lock virt_spin_lock -static inline bool virt_queued_spin_lock(struct qspinlock *lock) +static inline bool virt_spin_lock(struct qspinlock *lock) { if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) return false; - while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0) - cpu_relax(); + /* + * On hypervisors without PARAVIRT_SPINLOCKS support we fall + * back to a Test-and-Set spinlock, because fair locks have + * horrible lock 'holder' preemption issues. + */ + + do { + while (atomic_read(&lock->val) != 0) + cpu_relax(); + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); return true; } diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h index 83bfb87f5bf1..e2aadbc7151f 100644 --- a/include/asm-generic/qspinlock.h +++ b/include/asm-generic/qspinlock.h @@ -111,8 +111,8 @@ static inline void queued_spin_unlock_wait(struct qspinlock *lock) cpu_relax(); } -#ifndef virt_queued_spin_lock -static __always_inline bool virt_queued_spin_lock(struct qspinlock *lock) +#ifndef virt_spin_lock +static __always_inline bool virt_spin_lock(struct qspinlock *lock) { return false; } diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 337c8818541d..87e9ce6a63c5 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) if (pv_enabled()) goto queue; - if (virt_queued_spin_lock(lock)) + if (virt_spin_lock(lock)) return; /* Patches currently in stable-queue which might be from peterz@infradead.org are queue-4.2/time-fix-timekeeping_freqadjust-s-incorrect-use-of-abs-instead-of-abs64.patch queue-4.2/perf-x86-intel-fix-constraint-access.patch queue-4.2/sched-access-local-runqueue-directly-in-single_task_running.patch queue-4.2/locking-qspinlock-x86-only-emit-the-test-and-set-fallback-when-building-guest-support.patch queue-4.2/locking-qspinlock-x86-fix-performance-regression-under-unaccelerated-vms.patch