From: Tim Chen <tim.c.chen@linux.intel.com> To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@intel.com>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, Tim Chen <tim.c.chen@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org> Subject: [PATCH v3 4/5] rwsem/wake: check lock before do atomic update Date: Wed, 26 Jun 2013 09:28:01 -0700 [thread overview] Message-ID: <1372264081.22432.124.camel@schen9-DESK> (raw) In-Reply-To: <cover.1372261602.git.tim.c.chen@linux.intel.com> Atomic update lock and roll back will cause cache bouncing in large machine. A lock status pre-read can relieve this problem Suggested-by: Davidlohr bueso <davidlohr.bueso@hp.com> Suggested-by: Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by: Alex Shi <alex.shi@intel.com> --- lib/rwsem.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) diff --git a/lib/rwsem.c b/lib/rwsem.c index a8055cf..1d6e6e8 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -64,7 +64,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) struct rwsem_waiter *waiter; struct task_struct *tsk; struct list_head *next; - long oldcount, woken, loop, adjustment; + long woken, loop, adjustment; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->type == RWSEM_WAITING_FOR_WRITE) { @@ -86,6 +86,12 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) if (wake_type != RWSEM_WAKE_READ_OWNED) { adjustment = RWSEM_ACTIVE_READ_BIAS; while (1) { + long oldcount; + + /* A writer stole the lock. */ + if (unlikely(sem->count < RWSEM_WAITING_BIAS)) + return sem; + oldcount = rwsem_atomic_update(adjustment, sem) - adjustment; if (likely(oldcount >= RWSEM_WAITING_BIAS)) -- 1.7.4.4
WARNING: multiple messages have this Message-ID (diff)
From: Tim Chen <tim.c.chen@linux.intel.com> To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com>, Alex Shi <alex.shi@intel.com>, Andi Kleen <andi@firstfloor.org>, Michel Lespinasse <walken@google.com>, Davidlohr Bueso <davidlohr.bueso@hp.com>, Matthew R Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@intel.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Rik van Riel <riel@redhat.com>, Peter Hurley <peter@hurleysoftware.com>, Tim Chen <tim.c.chen@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org> Subject: [PATCH v3 4/5] rwsem/wake: check lock before do atomic update Date: Wed, 26 Jun 2013 09:28:01 -0700 [thread overview] Message-ID: <1372264081.22432.124.camel@schen9-DESK> (raw) In-Reply-To: <cover.1372261602.git.tim.c.chen@linux.intel.com> Atomic update lock and roll back will cause cache bouncing in large machine. A lock status pre-read can relieve this problem Suggested-by: Davidlohr bueso <davidlohr.bueso@hp.com> Suggested-by: Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by: Alex Shi <alex.shi@intel.com> --- lib/rwsem.c | 8 +++++++- 1 files changed, 7 insertions(+), 1 deletions(-) diff --git a/lib/rwsem.c b/lib/rwsem.c index a8055cf..1d6e6e8 100644 --- a/lib/rwsem.c +++ b/lib/rwsem.c @@ -64,7 +64,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) struct rwsem_waiter *waiter; struct task_struct *tsk; struct list_head *next; - long oldcount, woken, loop, adjustment; + long woken, loop, adjustment; waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list); if (waiter->type == RWSEM_WAITING_FOR_WRITE) { @@ -86,6 +86,12 @@ __rwsem_do_wake(struct rw_semaphore *sem, enum rwsem_wake_type wake_type) if (wake_type != RWSEM_WAKE_READ_OWNED) { adjustment = RWSEM_ACTIVE_READ_BIAS; while (1) { + long oldcount; + + /* A writer stole the lock. */ + if (unlikely(sem->count < RWSEM_WAITING_BIAS)) + return sem; + oldcount = rwsem_atomic_update(adjustment, sem) - adjustment; if (likely(oldcount >= RWSEM_WAITING_BIAS)) -- 1.7.4.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2013-06-26 16:28 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <cover.1372261602.git.tim.c.chen@linux.intel.com> 2013-06-26 16:27 ` [PATCH v3 1/5] rwsem: check the lock before cpmxchg in down_write_trylock Tim Chen 2013-06-26 16:27 ` Tim Chen 2013-06-26 16:27 ` [PATCH v3 2/5] rwsem: remove 'out' label in do_wake Tim Chen 2013-06-26 16:27 ` Tim Chen 2013-06-26 16:27 ` [PATCH v3 3/5] rwsem: remove try_reader_grant label do_wake Tim Chen 2013-06-26 16:27 ` Tim Chen 2013-06-26 16:28 ` Tim Chen [this message] 2013-06-26 16:28 ` [PATCH v3 4/5] rwsem/wake: check lock before do atomic update Tim Chen 2013-06-26 16:28 ` [PATCH v3 5/5] rwsem: do optimistic spinning for writer lock acquisition Tim Chen 2013-06-26 16:28 ` Tim Chen
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