All of lore.kernel.org
 help / color / mirror / Atom feed
From: Tim Chen <tim.c.chen@linux.intel.com>
To: Ingo Molnar <mingo@elte.hu>, Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alex Shi <alex.shi@linaro.org>, 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>,
	"Paul E.McKenney" <paulmck@linux.vnet.ibm.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>,
	linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock
Date: Wed, 02 Oct 2013 15:38:18 -0700	[thread overview]
Message-ID: <1380753498.11046.83.camel@schen9-DESK> (raw)
In-Reply-To: <cover.1380748401.git.tim.c.chen@linux.intel.com>

Cmpxchg will cause the cacheline bouning when do the value checking,
that cause scalability issue in a large machine (like a 80 core box).

So a lock pre-read can relief this contention.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
 include/asm-generic/rwsem.h |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index bb1e2cd..5ba80e7 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -70,11 +70,11 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
-	long tmp;
+	if (unlikely(sem->count != RWSEM_UNLOCKED_VALUE))
+		return 0;
 
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
+	return cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
+		      RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_UNLOCKED_VALUE;
 }
 
 /*
-- 
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: Linus Torvalds <torvalds@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Alex Shi <alex.shi@linaro.org>, 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>,
	"Paul E.McKenney" <paulmck@linux.vnet.ibm.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>,
	linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock
Date: Wed, 02 Oct 2013 15:38:18 -0700	[thread overview]
Message-ID: <1380753498.11046.83.camel@schen9-DESK> (raw)
In-Reply-To: <cover.1380748401.git.tim.c.chen@linux.intel.com>

Cmpxchg will cause the cacheline bouning when do the value checking,
that cause scalability issue in a large machine (like a 80 core box).

So a lock pre-read can relief this contention.

Signed-off-by: Alex Shi <alex.shi@intel.com>
---
 include/asm-generic/rwsem.h |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/rwsem.h b/include/asm-generic/rwsem.h
index bb1e2cd..5ba80e7 100644
--- a/include/asm-generic/rwsem.h
+++ b/include/asm-generic/rwsem.h
@@ -70,11 +70,11 @@ static inline void __down_write(struct rw_semaphore *sem)
 
 static inline int __down_write_trylock(struct rw_semaphore *sem)
 {
-	long tmp;
+	if (unlikely(sem->count != RWSEM_UNLOCKED_VALUE))
+		return 0;
 
-	tmp = cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
-		      RWSEM_ACTIVE_WRITE_BIAS);
-	return tmp == RWSEM_UNLOCKED_VALUE;
+	return cmpxchg(&sem->count, RWSEM_UNLOCKED_VALUE,
+		      RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_UNLOCKED_VALUE;
 }
 
 /*
-- 
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>

  parent reply	other threads:[~2013-10-02 22:38 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1380748401.git.tim.c.chen@linux.intel.com>
2013-10-02 22:38 ` [PATCH v8 0/9] rwsem performance optimizations Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-03  7:32   ` Ingo Molnar
2013-10-03  7:32     ` Ingo Molnar
2013-10-07 22:57     ` Tim Chen
2013-10-07 22:57       ` Tim Chen
2013-10-09  6:15       ` Ingo Molnar
2013-10-09  6:15         ` Ingo Molnar
2013-10-09  7:28         ` Peter Zijlstra
2013-10-09  7:28           ` Peter Zijlstra
2013-10-10  3:14           ` Linus Torvalds
2013-10-10  3:14             ` Linus Torvalds
2013-10-10  5:03             ` Davidlohr Bueso
2013-10-10  5:03               ` Davidlohr Bueso
2013-10-09 16:34         ` Tim Chen
2013-10-09 16:34           ` Tim Chen
2013-10-10  7:54           ` Ingo Molnar
2013-10-10  7:54             ` Ingo Molnar
2013-10-16  0:09             ` Tim Chen
2013-10-16  0:09               ` Tim Chen
2013-10-16  6:55               ` Ingo Molnar
2013-10-16  6:55                 ` Ingo Molnar
2013-10-16 18:28                 ` Tim Chen
2013-10-16 18:28                   ` Tim Chen
2013-11-04 22:36                   ` Tim Chen
2013-11-04 22:36                     ` Tim Chen
2013-10-16 21:55                 ` Tim Chen
2013-10-16 21:55                   ` Tim Chen
2013-10-18  6:52                   ` Ingo Molnar
2013-10-18  6:52                     ` Ingo Molnar
2013-10-02 22:38 ` Tim Chen [this message]
2013-10-02 22:38   ` [PATCH v8 1/9] rwsem: check the lock before cpmxchg in down_write_trylock Tim Chen
2013-10-02 22:38 ` [PATCH v8 2/9] rwsem: remove 'out' label in do_wake Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 3/9] rwsem: remove try_reader_grant label do_wake Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 4/9] rwsem/wake: check lock before do atomic update Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 5/9] MCS Lock: Restructure the MCS lock defines and locking code into its own file Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-08 19:51   ` Rafael Aquini
2013-10-08 19:51     ` Rafael Aquini
2013-10-08 20:34     ` Tim Chen
2013-10-08 20:34       ` Tim Chen
2013-10-08 21:31       ` Rafael Aquini
2013-10-08 21:31         ` Rafael Aquini
2013-10-02 22:38 ` [PATCH v8 6/9] MCS Lock: optimizations and extra comments Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 7/9] MCS Lock: Barrier corrections Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 8/9] rwsem: do optimistic spinning for writer lock acquisition Tim Chen
2013-10-02 22:38   ` Tim Chen
2013-10-02 22:38 ` [PATCH v8 9/9] rwsem: reduce spinlock contention in wakeup code path Tim Chen
2013-10-02 22:38   ` Tim Chen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1380753498.11046.83.camel@schen9-DESK \
    --to=tim.c.chen@linux.intel.com \
    --cc=Waiman.Long@hp.com \
    --cc=a.p.zijlstra@chello.nl \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=alex.shi@linaro.org \
    --cc=andi@firstfloor.org \
    --cc=dave.hansen@intel.com \
    --cc=davidlohr.bueso@hp.com \
    --cc=jason.low2@hp.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=matthew.r.wilcox@intel.com \
    --cc=mingo@elte.hu \
    --cc=paulmck@linux.vnet.ibm.com \
    --cc=peter@hurleysoftware.com \
    --cc=riel@redhat.com \
    --cc=torvalds@linux-foundation.org \
    --cc=walken@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.