Message-ID: <1370964165.9844.172.camel@gandalf.local.home>
Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock
From: Steven Rostedt <rostedt@goodmis.org>
To: paulmck@linux.vnet.ibm.com
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ingo Molnar <mingo@elte.hu>, Dipankar Sarma <dipankar@in.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Josh Triplett <josh@joshtriplett.org>, niv@us.ibm.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Valdis Kletnieks <Valdis.Kletnieks@vt.edu>,
        David Howells <dhowells@redhat.com>,
        Eric Dumazet <edumazet@google.com>, Darren Hart <darren@dvhart.com>,
        =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
        sbw@mit.edu
Date: Tue, 11 Jun 2013 11:22:45 -0400
In-Reply-To: <20130611101401.GC5146@linux.vnet.ibm.com>
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On Tue, 2013-06-11 at 03:14 -0700, Paul E. McKenney wrote:
>  
> > Off-topic, although I am in this community for several years,
> > I am not exactly clear with this problem.
> > 
> > 1) In general case, which lock is the most competitive in the kernel? what it protects for?
> > 2) In which special case, which lock is the most competitive in the kernel? what it protects for?
> > 3) In general case, which list is the most hot list?
> > 4) In which special case, which list is the most hot list?
> 
> Others would know better than I, but mmap_sem has been called out as a

If the contention is with mmap_sem, then I doubt this is going to help
much, as that's a sleeping rw semaphore. Now, rw semaphores are
implemented with raw spinlocks, but I doubt that would be the main point
of contention, compared to the sleeping part.

-- Steve

> prime offender for some workloads.  There is of course some debate as
> to whether the fault lies mmap_sem or with the workloads.  There have
> been some efforts to solve this one on LKML, plus some in academia have
> worked on this as well:
> 


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