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From: Will Deacon <will.deacon@arm.com>
To: Waiman Long <longman@redhat.com>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, peterz@infradead.org,
	mingo@kernel.org, boqun.feng@gmail.com,
	paulmck@linux.vnet.ibm.com
Subject: Re: [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath
Date: Fri, 27 Apr 2018 11:16:19 +0100	[thread overview]
Message-ID: <20180427101619.GB21705@arm.com> (raw)
In-Reply-To: <1adce90b-7627-ed71-fd34-bb33388790d5@redhat.com>

Hi Waiman,

On Thu, Apr 26, 2018 at 04:16:30PM -0400, Waiman Long wrote:
> On 04/26/2018 06:34 AM, Will Deacon wrote:
> > diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> > index 2711940429f5..2dbad2f25480 100644
> > --- a/kernel/locking/qspinlock_paravirt.h
> > +++ b/kernel/locking/qspinlock_paravirt.h
> > @@ -118,11 +118,6 @@ static __always_inline void set_pending(struct qspinlock *lock)
> >  	WRITE_ONCE(lock->pending, 1);
> >  }
> >  
> > -static __always_inline void clear_pending(struct qspinlock *lock)
> > -{
> > -	WRITE_ONCE(lock->pending, 0);
> > -}
> > -
> >  /*
> >   * The pending bit check in pv_queued_spin_steal_lock() isn't a memory
> >   * barrier. Therefore, an atomic cmpxchg_acquire() is used to acquire the
> 
> There is another clear_pending() function after the "#else /*
> _Q_PENDING_BITS == 8 */" line that need to be removed as well.

Bugger, sorry I missed that one. Is the >= 16K CPUs case supported elsewhere
in Linux? The x86 Kconfig appears to clamp NR_CPUS to 8192 iiuc.

Anyway, additional patch below. Ingo -- please can you apply this on top?

Thanks,

Will

--->8

>From ef6aa51e47047fe1a57dfdbe2f45caf63fa95be4 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@arm.com>
Date: Fri, 27 Apr 2018 10:40:13 +0100
Subject: [PATCH] locking/qspinlock: Remove duplicate clear_pending function
 from PV code

The native clear_pending function is identical to the PV version, so the
latter can simply be removed. This fixes the build for systems with >=
16K CPUs using the PV lock implementation.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Waiman Long <longman@redhat.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 kernel/locking/qspinlock_paravirt.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 25730b2ac022..5a0cf5f9008c 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -130,11 +130,6 @@ static __always_inline void set_pending(struct qspinlock *lock)
 	atomic_or(_Q_PENDING_VAL, &lock->val);
 }
 
-static __always_inline void clear_pending(struct qspinlock *lock)
-{
-	atomic_andnot(_Q_PENDING_VAL, &lock->val);
-}
-
 static __always_inline int trylock_clear_pending(struct qspinlock *lock)
 {
 	int val = atomic_read(&lock->val);
-- 
2.1.4

  reply	other threads:[~2018-04-27 10:16 UTC|newest]

Thread overview: 41+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-26 10:34 [PATCH v3 00/14] kernel/locking: qspinlock improvements Will Deacon
2018-04-26 10:34 ` [PATCH v3 01/14] barriers: Introduce smp_cond_load_relaxed and atomic_cond_read_relaxed Will Deacon
2018-04-27  9:36   ` [tip:locking/core] locking/barriers: Introduce smp_cond_load_relaxed() and atomic_cond_read_relaxed() tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 02/14] locking/qspinlock: Merge struct __qspinlock into struct qspinlock Will Deacon
2018-04-27  9:37   ` [tip:locking/core] locking/qspinlock: Merge 'struct __qspinlock' into 'struct qspinlock' tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 03/14] locking/qspinlock: Bound spinning on pending->locked transition in slowpath Will Deacon
2018-04-27  9:37   ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 04/14] locking/qspinlock/x86: Increase _Q_PENDING_LOOPS upper bound Will Deacon
2018-04-27  9:38   ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Will Deacon
2018-04-26 15:53   ` Peter Zijlstra
2018-04-26 16:55     ` Will Deacon
2018-04-28 12:45       ` Peter Zijlstra
2018-04-30  8:53         ` Will Deacon
2018-04-26 20:16   ` Waiman Long
2018-04-27 10:16     ` Will Deacon [this message]
2018-04-27 11:01       ` [tip:locking/core] locking/qspinlock: Remove duplicate clear_pending() function from PV code tip-bot for Will Deacon
2018-04-27 13:09       ` [PATCH v3 05/14] locking/qspinlock: Remove unbounded cmpxchg loop from locking slowpath Waiman Long
2018-04-27  9:39   ` [tip:locking/core] locking/qspinlock: Remove unbounded cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 06/14] locking/qspinlock: Kill cmpxchg loop when claiming lock from head of queue Will Deacon
2018-04-27  9:39   ` [tip:locking/core] locking/qspinlock: Kill cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 07/14] locking/qspinlock: Use atomic_cond_read_acquire Will Deacon
2018-04-27  9:40   ` [tip:locking/core] locking/qspinlock: Use atomic_cond_read_acquire() tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 08/14] locking/mcs: Use smp_cond_load_acquire() in mcs spin loop Will Deacon
2018-04-27  9:40   ` [tip:locking/core] locking/mcs: Use smp_cond_load_acquire() in MCS " tip-bot for Jason Low
2018-04-26 10:34 ` [PATCH v3 09/14] locking/qspinlock: Use smp_cond_load_relaxed to wait for next node Will Deacon
2018-04-27  9:41   ` [tip:locking/core] locking/qspinlock: Use smp_cond_load_relaxed() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 10/14] locking/qspinlock: Make queued_spin_unlock use smp_store_release Will Deacon
2018-04-27  9:42   ` [tip:locking/core] locking/qspinlock: Use smp_store_release() in queued_spin_unlock() tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 11/14] locking/qspinlock: Elide back-to-back RELEASE operations with smp_wmb() Will Deacon
2018-04-27  9:42   ` [tip:locking/core] " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 12/14] locking/qspinlock: Use try_cmpxchg instead of cmpxchg when locking Will Deacon
2018-04-27  9:43   ` [tip:locking/core] locking/qspinlock: Use try_cmpxchg() instead of cmpxchg() " tip-bot for Will Deacon
2018-04-26 10:34 ` [PATCH v3 13/14] locking/qspinlock: Add stat tracking for pending vs slowpath Will Deacon
2018-04-27  9:43   ` [tip:locking/core] locking/qspinlock: Add stat tracking for pending vs. slowpath tip-bot for Waiman Long
2018-04-26 10:34 ` [PATCH v3 14/14] MAINTAINERS: Add myself as a co-maintainer for LOCKING PRIMITIVES Will Deacon
2018-04-26 15:55   ` Peter Zijlstra
2018-04-27  9:44   ` [tip:locking/core] MAINTAINERS: Add myself as a co-maintainer for the locking subsystem tip-bot for Will Deacon
2018-04-26 15:54 ` [PATCH v3 00/14] kernel/locking: qspinlock improvements Peter Zijlstra
2018-04-27  9:33   ` Ingo Molnar
2018-04-26 20:18 ` Waiman Long

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