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Message-ID: <20130722103402.GA1991@gmail.com>
Date: Mon, 22 Jul 2013 12:34:02 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Waiman Long <waiman.long@...com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
linux-arch@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Richard Weinberger <richard@....at>,
Catalin Marinas <catalin.marinas@....com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Matt Fleming <matt.fleming@...el.com>,
Herbert Xu <herbert@...dor.apana.org.au>,
Akinobu Mita <akinobu.mita@...il.com>,
Rusty Russell <rusty@...tcorp.com.au>,
Michel Lespinasse <walken@...gle.com>,
Andi Kleen <andi@...stfloor.org>,
Rik van Riel <riel@...hat.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Chandramouleeswaran, Aswin" <aswin@...com>,
"Norton, Scott J" <scott.norton@...com>,
George Spelvin <linux@...izon.com>
Subject: Re: [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation
* Waiman Long <waiman.long@...com> wrote:
> I had run some performance tests using the fserver and new_fserver
> benchmarks (on ext4 filesystems) of the AIM7 test suite on a 80-core
> DL980 with HT on. The following kernels were used:
>
> 1. Modified 3.10.1 kernel with mb_cache_spinlock in fs/mbcache.c
> replaced by a rwlock
> 2. Modified 3.10.1 kernel + modified __read_lock_failed code as suggested
> by Ingo
> 3. Modified 3.10.1 kernel + queue read/write lock
> 4. Modified 3.10.1 kernel + queue read/write lock in classic read/write
> lock behavior
>
> The last one is with the read lock stealing flag set in the qrwlock
> structure to give priority to readers and behave more like the classic
> read/write lock with less fairness.
>
> The following table shows the averaged results in the 200-1000
> user ranges:
>
> +-----------------+--------+--------+--------+--------+
> | Kernel | 1 | 2 | 3 | 4 |
> +-----------------+--------+--------+--------+--------+
> | fserver JPM | 245598 | 274457 | 403348 | 411941 |
> | % change from 1 | 0% | +11.8% | +64.2% | +67.7% |
> +-----------------+--------+--------+--------+--------+
> | new-fserver JPM | 231549 | 269807 | 399093 | 399418 |
> | % change from 1 | 0% | +16.5% | +72.4% | +72.5% |
> +-----------------+--------+--------+--------+--------+
So it's not just herding that is a problem.
I'm wondering, how sensitive is this particular benchmark to fairness?
I.e. do the 200-1000 simulated users each perform the same number of ops,
so that any smearing of execution time via unfairness gets amplified?
I.e. does steady-state throughput go up by 60%+ too with your changes?
Thanks,
Ingo
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