From: Manfred Spraul <manfred@colorfullife.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org,
netfilter-devel@vger.kernel.org, netdev@vger.kernel.org,
oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com,
dave@stgolabs.net, tj@kernel.org, arnd@arndb.de,
linux-arch@vger.kernel.org, will.deacon@arm.com,
peterz@infradead.org, parri.andrea@gmail.com,
torvalds@linux-foundation.org,
Pablo Neira Ayuso <pablo@netfilter.org>,
Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>,
Florian Westphal <fw@strlen.de>,
"David S. Miller" <davem@davemloft.net>,
coreteam@netfilter.org, 1vier1@web.de
Subject: Re: [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair
Date: Thu, 6 Jul 2017 20:43:28 +0200 [thread overview]
Message-ID: <ee509620-8ba5-be45-743e-f077a457c01d@colorfullife.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1707031543170.2027-100000@iolanthe.rowland.org>
[-- Attachment #1: Type: text/plain, Size: 519 bytes --]
Hi Alan,
On 07/03/2017 09:57 PM, Alan Stern wrote:
>
> (Alternatively, you could make nf_conntrack_all_unlock() do a
> lock+unlock on all the locks in the array, just like
> nf_conntrack_all_lock(). But of course, that would be a lot less
> efficient.)
Hmmmm.
Someone with a weakly ordered system who can test this?
semop() has a very short hotpath.
Either with aim9.shared_memory.ops_per_sec or
#sem-scalebench -t 10 -m 0
https://github.com/manfred-colorfu/ipcscale/blob/master/sem-scalebench.cpp
--
Manfred
[-- Attachment #2: 0002-ipc-sem.c-avoid-smp_load_acuqire-in-the-hot-path.patch --]
[-- Type: text/x-patch, Size: 3330 bytes --]
>From b549e0281b66124b62aa94543f91b0e616abaf52 Mon Sep 17 00:00:00 2001
From: Manfred Spraul <manfred@colorfullife.com>
Date: Thu, 6 Jul 2017 20:05:44 +0200
Subject: [PATCH 2/2] ipc/sem.c: avoid smp_load_acuqire() in the hot-path
Alan Stern came up with an interesting idea:
If we perform a spin_lock()/spin_unlock() pair in the slow path, then
we can skip the smp_load_acquire() in the hot path.
What do you think?
* When we removed the smp_mb() from the hot path, it was a user space
visible speed-up of 11%:
https://lists.01.org/pipermail/lkp/2017-February/005520.html
* On x86, there is no improvement - as smp_load_acquire is READ_ONCE().
* Slowing down the slow path should not hurt:
Due to the hysteresis code, the slow path is at least factor 10
rarer than it was before.
Especially: Who is able to test it?
Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Alan Stern <stern@rowland.harvard.edu>
---
ipc/sem.c | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)
diff --git a/ipc/sem.c b/ipc/sem.c
index 947dc23..75a4358 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -186,16 +186,15 @@ static int sysvipc_sem_proc_show(struct seq_file *s, void *it);
* * either local or global sem_lock() for read.
*
* Memory ordering:
- * Most ordering is enforced by using spin_lock() and spin_unlock().
+ * All ordering is enforced by using spin_lock() and spin_unlock().
* The special case is use_global_lock:
* Setting it from non-zero to 0 is a RELEASE, this is ensured by
- * using smp_store_release().
- * Testing if it is non-zero is an ACQUIRE, this is ensured by using
- * smp_load_acquire().
- * Setting it from 0 to non-zero must be ordered with regards to
- * this smp_load_acquire(), this is guaranteed because the smp_load_acquire()
- * is inside a spin_lock() and after a write from 0 to non-zero a
- * spin_lock()+spin_unlock() is done.
+ * performing spin_lock()/spin_lock() on every semaphore before setting to
+ * non-zero.
+ * Setting it from 0 to non-zero is an ACQUIRE, this is ensured by
+ * performing spin_lock()/spin_lock() on every semaphore after setting to
+ * non-zero.
+ * Testing if it is non-zero is within spin_lock(), no need for a barrier.
*/
#define sc_semmsl sem_ctls[0]
@@ -325,13 +324,20 @@ static void complexmode_tryleave(struct sem_array *sma)
return;
}
if (sma->use_global_lock == 1) {
+ int i;
+ struct sem *sem;
/*
* Immediately after setting use_global_lock to 0,
- * a simple op can start. Thus: all memory writes
- * performed by the current operation must be visible
- * before we set use_global_lock to 0.
+ * a simple op can start.
+ * Perform a full lock/unlock, to guarantee memory
+ * ordering.
*/
- smp_store_release(&sma->use_global_lock, 0);
+ for (i = 0; i < sma->sem_nsems; i++) {
+ sem = sma->sem_base + i;
+ spin_lock(&sem->lock);
+ spin_unlock(&sem->lock);
+ }
+ sma->use_global_lock = 0;
} else {
sma->use_global_lock--;
}
@@ -379,8 +385,7 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops,
*/
spin_lock(&sem->lock);
- /* pairs with smp_store_release() */
- if (!smp_load_acquire(&sma->use_global_lock)) {
+ if (!sma->use_global_lock) {
/* fast path successful! */
return sops->sem_num;
}
--
2.9.4
next prev parent reply other threads:[~2017-07-06 18:43 UTC|newest]
Thread overview: 122+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-29 23:59 [PATCH RFC 0/26] Remove spin_unlock_wait() Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 01/26] netfilter: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
[not found] ` <a6642feb-2f3a-980f-5ed6-2deb79563e6b@colorfullife.com>
2017-07-02 2:00 ` Paul E. McKenney
2017-07-03 14:39 ` Alan Stern
2017-07-03 17:14 ` Paul E. McKenney
2017-07-03 19:01 ` Manfred Spraul
2017-07-03 19:57 ` Alan Stern
2017-07-06 18:43 ` Manfred Spraul [this message]
2017-07-03 20:04 ` Alan Stern
2017-07-03 20:53 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 02/26] task_work: " Paul E. McKenney
2017-06-30 11:04 ` Oleg Nesterov
2017-06-30 12:50 ` Paul E. McKenney
2017-06-30 15:20 ` Oleg Nesterov
2017-06-30 16:16 ` Paul E. McKenney
2017-06-30 17:21 ` Paul E. McKenney
2017-06-30 19:21 ` Oleg Nesterov
2017-06-30 19:50 ` Alan Stern
2017-06-30 20:04 ` Paul E. McKenney
2017-06-30 20:02 ` Paul E. McKenney
2017-06-30 20:19 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 03/26] sched: " Paul E. McKenney
2017-06-30 10:31 ` Arnd Bergmann
2017-06-30 12:35 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 04/26] completion: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 05/26] exit: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 07/26] drivers/ata: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 08/26] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-06-30 9:19 ` Will Deacon
2017-06-30 12:38 ` Paul E. McKenney
2017-06-30 13:13 ` Will Deacon
2017-06-30 22:18 ` Paul E. McKenney
2017-07-03 13:15 ` Will Deacon
2017-07-03 16:18 ` Paul E. McKenney
2017-07-03 16:40 ` Linus Torvalds
2017-07-03 17:13 ` Will Deacon
2017-07-03 22:30 ` Paul E. McKenney
2017-07-03 22:49 ` Linus Torvalds
2017-07-04 0:39 ` Paul E. McKenney
2017-07-04 0:54 ` Paul E. McKenney
2017-07-03 21:10 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 09/26] alpha: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 10/26] arc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 11/26] arm: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 12/26] arm64: " Paul E. McKenney
2017-06-30 9:20 ` Will Deacon
2017-06-30 17:29 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 13/26] blackfin: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 14/26] hexagon: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 15/26] ia64: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 16/26] m32r: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 18/26] mips: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 19/26] mn10300: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 20/26] parisc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 21/26] powerpc: " Paul E. McKenney
2017-07-02 3:58 ` Boqun Feng
2017-07-05 23:57 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 22/26] s390: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 23/26] sh: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 24/26] sparc: " Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 25/26] tile: " Paul E. McKenney
2017-06-30 0:06 ` Linus Torvalds
2017-06-30 0:09 ` Paul E. McKenney
2017-06-30 0:14 ` Paul E. McKenney
2017-06-30 0:10 ` Linus Torvalds
2017-06-30 0:24 ` Paul E. McKenney
2017-06-30 0:01 ` [PATCH RFC 26/26] xtensa: " Paul E. McKenney
[not found] ` <1498780894-8253-6-git-send-email-paulmck@linux.vnet.ibm.com>
2017-07-01 19:23 ` [PATCH RFC 06/26] ipc: Replace spin_unlock_wait() with lock/unlock pair Manfred Spraul
2017-07-02 3:16 ` Paul E. McKenney
2017-07-05 23:29 ` [PATCH v2 0/9] Remove spin_unlock_wait() Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Paul E. McKenney
2017-07-06 18:45 ` Manfred Spraul
2017-07-06 20:26 ` Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 2/9] task_work: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 3/9] sched: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 4/9] completion: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 5/9] exit: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 6/9] ipc: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 7/9] drivers/ata: " Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 8/9] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-07-05 23:31 ` [PATCH v2 9/9] arch: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
2017-07-06 14:12 ` [PATCH v2 0/9] Remove spin_unlock_wait() David Laight
2017-07-06 15:21 ` Paul E. McKenney
2017-07-06 16:10 ` Peter Zijlstra
2017-07-06 16:24 ` Paul E. McKenney
2017-07-06 16:41 ` Peter Zijlstra
2017-07-06 17:03 ` Paul E. McKenney
2017-07-06 16:49 ` Alan Stern
2017-07-06 16:54 ` Peter Zijlstra
2017-07-06 19:37 ` Alan Stern
2017-07-06 16:05 ` Peter Zijlstra
2017-07-06 16:20 ` Paul E. McKenney
2017-07-06 16:50 ` Peter Zijlstra
2017-07-06 17:08 ` Will Deacon
2017-07-06 17:29 ` Paul E. McKenney
2017-07-06 17:18 ` Paul E. McKenney
2017-07-07 8:31 ` Ingo Molnar
2017-07-07 8:44 ` Peter Zijlstra
2017-07-07 10:33 ` Ingo Molnar
2017-07-07 11:23 ` Peter Zijlstra
2017-07-07 14:41 ` Paul E. McKenney
2017-07-08 8:43 ` Ingo Molnar
2017-07-08 11:41 ` Paul E. McKenney
2017-07-07 17:47 ` Manfred Spraul
2017-07-08 8:35 ` Ingo Molnar
2017-07-08 11:39 ` Paul E. McKenney
2017-07-08 12:30 ` Ingo Molnar
2017-07-08 14:45 ` Paul E. McKenney
2017-07-08 16:21 ` Alan Stern
2017-07-10 17:22 ` Manfred Spraul
2017-07-07 8:06 ` Ingo Molnar
2017-07-07 9:32 ` Ingo Molnar
2017-07-07 19:27 ` [PATCH v3 " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 2/9] task_work: Replace spin_unlock_wait() with lock/unlock pair Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 3/9] sched: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 4/9] completion: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 5/9] exit: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 6/9] ipc: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 7/9] drivers/ata: " Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 8/9] locking: Remove spin_unlock_wait() generic definitions Paul E. McKenney
2017-07-07 19:28 ` [PATCH v3 9/9] arch: Remove spin_unlock_wait() arch-specific definitions Paul E. McKenney
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