From: Waiman Long <waiman.long@hp.com>
To: Andi Kleen <andi@firstfloor.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Jeff Layton <jlayton@redhat.com>,
Miklos Szeredi <mszeredi@suse.cz>, Ingo Molnar <mingo@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"Chandramouleeswaran, Aswin" <aswin@hp.com>,
"Norton, Scott J" <scott.norton@hp.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH v2 1/2] spinlock: New spinlock_refcount.h for lockless update of refcount
Date: Wed, 26 Jun 2013 21:15:31 -0400 [thread overview]
Message-ID: <51CB9233.7020508@hp.com> (raw)
In-Reply-To: <20130627010658.GL6123@two.firstfloor.org>
On 06/26/2013 09:06 PM, Andi Kleen wrote:
>> In the uncontended case, doing spin_unlock_wait will be similar to
>> spin_can_lock. This, when combined with a cmpxchg, is still faster
>> than doing 2 atomic operations in spin_lock/spin_unlock.
> I'm totally against any new users of spin_unlock_wait()
>
> It has bizarre semantics, most likely will make various
> lock optimizations impossible, it's race condition hell
> for most users etc.
>
> spin_can_lock() is not quite as bad has a lot of the similar problems.
>
>> BTW, spin_can_lock is just the negation of spin_is_locked.
> e.g. with elision it's not.
>
> -Andi
OK, it is about Haswell's lock elision feature. I will see what I can do
to remove those problematic function calls.
Regards,
Longman
next prev parent reply other threads:[~2013-06-27 1:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-26 17:43 [PATCH v2 0/2] Lockless update of reference count protected by spinlock Waiman Long
2013-06-26 17:43 ` [PATCH v2 1/2] spinlock: New spinlock_refcount.h for lockless update of refcount Waiman Long
2013-06-26 20:17 ` Andi Kleen
2013-06-26 21:07 ` Waiman Long
2013-06-26 21:22 ` Andi Kleen
2013-06-26 23:26 ` Waiman Long
2013-06-27 1:06 ` Andi Kleen
2013-06-27 1:15 ` Waiman Long [this message]
2013-06-27 1:24 ` Waiman Long
2013-06-27 1:37 ` Andi Kleen
2013-06-27 14:56 ` Waiman Long
2013-06-28 13:46 ` Thomas Gleixner
2013-06-29 20:30 ` Waiman Long
2013-06-26 23:27 ` Thomas Gleixner
2013-06-26 23:06 ` Thomas Gleixner
2013-06-27 0:16 ` Waiman Long
2013-06-27 14:44 ` Thomas Gleixner
2013-06-29 21:03 ` Waiman Long
2013-06-27 0:26 ` Waiman Long
2013-06-29 17:45 ` Linus Torvalds
2013-06-29 20:23 ` Waiman Long
2013-06-29 21:34 ` Waiman Long
2013-06-29 22:11 ` Linus Torvalds
2013-06-29 22:34 ` Waiman Long
2013-06-29 21:58 ` Linus Torvalds
2013-06-29 22:47 ` Linus Torvalds
2013-07-01 13:40 ` Waiman Long
2013-06-26 17:43 ` [PATCH v2 2/2] dcache: Locklessly update d_count whenever possible Waiman Long
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