linux-kernel - Re: [PATCH RFC ticketlock] Auto-queued ticketlock

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Date:	Tue, 11 Jun 2013 11:05:26 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Davidlohr Bueso <davidlohr.bueso@...com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	赖江山 <laijs@...fujitsu.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Josh Triplett <josh@...htriplett.org>, niv@...ibm.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Valdis Kletnieks <Valdis.Kletnieks@...edu>,
	David Howells <dhowells@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Darren Hart <darren@...art.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	sbw@....edu
Subject: Re: [PATCH RFC ticketlock] Auto-queued ticketlock

On Tue, Jun 11, 2013 at 10:53:06AM -0700, Davidlohr Bueso wrote:
> On Mon, 2013-06-10 at 17:51 -0700, Linus Torvalds wrote:
> > On Mon, Jun 10, 2013 at 5:44 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> > >
> > > OK, I haven't found a issue here yet, but youss are beiing trickssy! We
> > > don't like trickssy, and we must find precccciouss!!!
> > 
> > .. and I personally have my usual reservations. I absolutely hate
> > papering over scalability issues, and historically whenever people
> > have ever thought that we want complex spinlocks, the problem has
> > always been that the locking sucks.
> > 
> > So reinforced by previous events, I really feel that code that needs
> > this kind of spinlock is broken and needs to be fixed, rather than
> > actually introduce tricky spinlocks.
> > 
> > So in order to merge something like this, I want (a) numbers for real
> > loads and (b) explanations for why the spinlock users cannot be fixed.
> 
> I hate to be the bearer of bad news but I got some pretty bad aim7
> performance numbers with this patch on an 8-socket (80 core) 256 Gb
> memory DL980 box against a vanilla 3.10-rc4 kernel:

Looks pretty ugly, sorry that it doesn't help in many of your situations.

Any info on what bottlenecks you are encountering?

							Thanx, Paul

> * shared workload: 
> 10-100 users is in the noise area.
> 100-2000 users: -13% throughput.
> 
> * high_systime workload: 
> 10-700 users is in the noise area.
> 700-2000 users: -55% throughput.
> 
> * disk:
> 10-100 users -57% throughput.
> 100-1000 users: -25% throughput
> 1000-2000 users: +8% throughput (this patch only benefits when we have a
> lot of concurrency).
> 
> * custom:
> 10-100 users: -33% throughput.
> 100-2000 users: -46% throughput.
> 
> * alltests:
> 10-1000 users is in the noise area.
> 1000-2000 users: -10% throughput.
> 
> One notable exception is the short workload where we actually see
> positive numbers:
> 10-100 users: +40% throughput.
> 100-2000 users: +69% throughput.
> 
> Thanks,
> Davidlohr
> 

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