linux-kernel - Re: [RFC][PATCH 0/3] locking/mutex: Rewrite basic mutex

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Date:   Tue, 23 Aug 2016 18:13:43 -0700
From:   Jason Low <jason.low2@....com>
To:     Davidlohr Bueso <dave@...olabs.net>
Cc:     jason.low2@....com, Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Waiman Long <waiman.long@....com>,
        Ding Tianhong <dingtianhong@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <Will.Deacon@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Imre Deak <imre.deak@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        "Paul E. McKenney" <paulmck@...ibm.com>, jason.low2@...com
Subject: Re: [RFC][PATCH 0/3] locking/mutex: Rewrite basic mutex

On Tue, 2016-08-23 at 09:35 -0700, Jason Low wrote:
> On Tue, 2016-08-23 at 09:17 -0700, Davidlohr Bueso wrote:
> > I have not looked at the patches yet, but are there any performance minutia
> > to be aware of?
> 
> This would remove all of the mutex architecture specific optimizations
> in the (common) fastpath, so that is one thing that could reduce
> performance. I'll run some benchmarks to see what some of the
> performance impacts of these patches would be.

I tested this patch on an 8 socket system with the high_systime AIM7
workload with diskfs. The patch provided big performance improvements in
terms of throughput in the highly contended cases.

-------------------------------------------------
|  users      | avg throughput | avg throughput |
              | without patch  | with patch     |
-------------------------------------------------
| 10 - 90     |   13,943 JPM   |   14,432 JPM   |
-------------------------------------------------
| 100 - 900   |   75,475 JPM   |  102,922 JPM   |
-------------------------------------------------
| 1000 - 1900 |   77,299 JPM   |  115,271 JPM   |
-------------------------------------------------

Unfortunately, at 2000 users, the modified kernel locked up.

# INFO: task reaim:<#> blocked for more than 120 seconds.

So something appears to be buggy.