From: Davidlohr Bueso <dave@stgolabs.net>
To: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
linux-kernel@vger.kernel.org, tglx@linutronix.de
Subject: Re: [PATCH] locking/rtmutex: remove unused cmpxchg_relaxed
Date: Fri, 31 Jan 2020 09:39:22 -0800 [thread overview]
Message-ID: <20200131173922.hjvugxuybrn2wbsn@linux-p48b> (raw)
In-Reply-To: <1579595686-251535-1-git-send-email-alex.shi@linux.alibaba.com>
Cc'ing tglx.
On Tue, 21 Jan 2020, Alex Shi wrote:
>No one use this macro after it was introduced. Better to remove it?
You also need to remove it for the CONFIG_DEBUG_RT_MUTEXES=y case.
>
>Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
>Cc: Peter Zijlstra <peterz@infradead.org>
>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 | 1 -
> 1 file changed, 1 deletion(-)
>
>diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
>index 851bbb10819d..a849964a348d 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)
Hmm unrelated, but do we want CCAS for rtmutex fastpath? Ie:
(l->owner == c && cmpxchg_acquire(&l->owner, c, n) == c)
That would optimize for the contended case and avoid the cmpxchg - it would
also help if we ever do the top-waiter spin thing.
Thanks,
Davidlohr
next prev parent reply other threads:[~2020-01-31 17:49 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-21 8:34 [PATCH] locking/rtmutex: remove unused cmpxchg_relaxed Alex Shi
2020-01-31 17:39 ` Davidlohr Bueso [this message]
2020-01-31 20:23 ` Thomas Gleixner
2020-02-04 10:18 ` Alex Shi
2020-02-12 15:07 ` Davidlohr Bueso
2020-02-14 15:17 ` [PATCH 1/2] locking/rtmutex: Remove unused rt_mutex_cmpxchg_relaxed() Alex Shi
2020-02-14 15:17 ` [PATCH 2/2] locking/rtmutex: optimize rt_mutex_cmpxchgs Alex Shi
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