* [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs
2020-04-17 14:50 [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
@ 2020-04-17 14:50 ` Alex Shi
2020-04-26 16:31 ` Thomas Gleixner
2020-04-26 12:05 ` [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
` (2 subsequent siblings)
3 siblings, 1 reply; 6+ messages in thread
From: Alex Shi @ 2020-04-17 14:50 UTC (permalink / raw)
Cc: Alex Shi, Thomas Gleixner, Davidlohr Bueso, Ingo Molnar,
Will Deacon, linux-kernel
Checking l->owner first to skip time cost cmpxchgs.
Suggested-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-kernel@vger.kernel.org
---
kernel/locking/rtmutex.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index cfdd5b93264d..232727a4a220 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -141,8 +141,10 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
* set up.
*/
#ifndef CONFIG_DEBUG_RT_MUTEXES
-# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
-# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_acquire(l, c, n) \
+ (l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c)
+# define rt_mutex_cmpxchg_release(l, c, n) \
+ (l->owner == c && cmpxchg_release(&l->owner, c, n) == c)
/*
* Callers must hold the ->wait_lock -- which is the whole purpose as we force
--
1.8.3.1
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs
2020-04-17 14:50 ` [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs Alex Shi
@ 2020-04-26 16:31 ` Thomas Gleixner
0 siblings, 0 replies; 6+ messages in thread
From: Thomas Gleixner @ 2020-04-26 16:31 UTC (permalink / raw)
To: Alex Shi
Cc: Davidlohr Bueso, Ingo Molnar, Will Deacon, linux-kernel, Peter Zijlstra
Alex Shi <alex.shi@linux.alibaba.com> writes:
> Checking l->owner first to skip time cost cmpxchgs.
I don't see what that buys.
It actually adds an extra conditional in the non-contended case, which
is the case we are optimizing for.
In the contended case, i.e. when l->owner != c the cmpxchg cost is
completely irrelevant compared to the slowpath costs.
> #ifndef CONFIG_DEBUG_RT_MUTEXES
> -# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
> -# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
> +# define rt_mutex_cmpxchg_acquire(l, c, n) \
> + (l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c)
> +# define rt_mutex_cmpxchg_release(l, c, n) \
> + (l->owner == c && cmpxchg_release(&l->owner, c, n) == c)
This kind of micro-optimizing is more than dubious especially w/o
numbers backing up the benefit.
Thanks,
tglx
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
2020-04-17 14:50 [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
2020-04-17 14:50 ` [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs Alex Shi
@ 2020-04-26 12:05 ` Alex Shi
2020-04-26 20:04 ` [tip: locking/core] " tip-bot2 for Alex Shi
2020-04-27 10:45 ` tip-bot2 for Alex Shi
3 siblings, 0 replies; 6+ messages in thread
From: Alex Shi @ 2020-04-26 12:05 UTC (permalink / raw)
To: Thomas Gleixner, Davidlohr Bueso; +Cc: Ingo Molnar, Will Deacon, linux-kernel
This 2 small patches may missed for a few time.
Is it ok to be merged?
Thanks
Alex
在 2020/4/17 下午10:50, Alex Shi 写道:
> This macro isn't interested by anyone, so remove it.
>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Davidlohr Bueso <dave@stgolabs.net>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: linux-kernel@vger.kernel.org
> ---
> kernel/locking/rtmutex.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index c9f090d64f00..cfdd5b93264d 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -141,7 +141,6 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
> * set up.
> */
> #ifndef CONFIG_DEBUG_RT_MUTEXES
> -# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
> # define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
> # define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
>
> @@ -202,7 +201,6 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
> }
>
> #else
> -# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
> # define rt_mutex_cmpxchg_acquire(l,c,n) (0)
> # define rt_mutex_cmpxchg_release(l,c,n) (0)
>
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [tip: locking/core] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
2020-04-17 14:50 [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
2020-04-17 14:50 ` [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs Alex Shi
2020-04-26 12:05 ` [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
@ 2020-04-26 20:04 ` tip-bot2 for Alex Shi
2020-04-27 10:45 ` tip-bot2 for Alex Shi
3 siblings, 0 replies; 6+ messages in thread
From: tip-bot2 for Alex Shi @ 2020-04-26 20:04 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Alex Shi, Thomas Gleixner, x86, LKML
The following commit has been merged into the locking/core branch of tip:
Commit-ID: 2f879e9f05f7806d0885b57532831176204e411f
Gitweb: https://git.kernel.org/tip/2f879e9f05f7806d0885b57532831176204e411f
Author: Alex Shi <alex.shi@linux.alibaba.com>
AuthorDate: Fri, 17 Apr 2020 22:50:31 +08:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Sun, 26 Apr 2020 21:58:42 +02:00
locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1587135032-188866-1-git-send-email-alex.shi@linux.alibaba.com
---
kernel/locking/rtmutex.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 851bbb1..7ad22ea 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -141,7 +141,6 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
* set up.
*/
#ifndef CONFIG_DEBUG_RT_MUTEXES
-# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
@@ -202,7 +201,6 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
}
#else
-# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
# define rt_mutex_cmpxchg_release(l,c,n) (0)
^ permalink raw reply [flat|nested] 6+ messages in thread
* [tip: locking/core] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
2020-04-17 14:50 [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
` (2 preceding siblings ...)
2020-04-26 20:04 ` [tip: locking/core] " tip-bot2 for Alex Shi
@ 2020-04-27 10:45 ` tip-bot2 for Alex Shi
3 siblings, 0 replies; 6+ messages in thread
From: tip-bot2 for Alex Shi @ 2020-04-27 10:45 UTC (permalink / raw)
To: linux-tip-commits; +Cc: Alex Shi, Thomas Gleixner, x86, LKML
The following commit has been merged into the locking/core branch of tip:
Commit-ID: 23b5ae2e8e1326c91b5dfdbb6ebcd5a6820074ae
Gitweb: https://git.kernel.org/tip/23b5ae2e8e1326c91b5dfdbb6ebcd5a6820074ae
Author: Alex Shi <alex.shi@linux.alibaba.com>
AuthorDate: Fri, 17 Apr 2020 22:50:31 +08:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Mon, 27 Apr 2020 12:26:40 +02:00
locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed()
Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/1587135032-188866-1-git-send-email-alex.shi@linux.alibaba.com
---
kernel/locking/rtmutex.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index c9f090d..cfdd5b9 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -141,7 +141,6 @@ static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
* set up.
*/
#ifndef CONFIG_DEBUG_RT_MUTEXES
-# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
@@ -202,7 +201,6 @@ static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
}
#else
-# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
# define rt_mutex_cmpxchg_release(l,c,n) (0)
^ permalink raw reply [flat|nested] 6+ messages in thread