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Message-ID: <1472001223.2381.96.camel@j-VirtualBox>
Subject: Re: [RFC][PATCH 0/3] locking/mutex: Rewrite basic mutex
From: Jason Low <jason.low2@hpe.com>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: jason.low2@hpe.com, Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Waiman Long <waiman.long@hpe.com>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <Will.Deacon@arm.com>, Ingo Molnar <mingo@redhat.com>,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        "Paul E. McKenney" <paulmck@us.ibm.com>, jason.low2@hp.com
Date: Tue, 23 Aug 2016 18:13:43 -0700
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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.