From: Waiman Long <waiman.long@hp.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
George Spelvin <linux@horizon.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
aswin@hp.com, Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation
Date: Wed, 05 Feb 2014 22:08:35 -0500 [thread overview]
Message-ID: <52F2FCB3.7090400@hp.com> (raw)
In-Reply-To: <20140202090357.GA1006@gmail.com>
On 02/02/2014 04:03 AM, Ingo Molnar wrote:
> * Waiman Long<waiman.long@hp.com> wrote:
>
>> How about making the selection of MCS or ticket queuing either user
>> configurable or depending on the setting of NR_CPUS, NUMA, etc?
> No!
>
> There are lots of disadvantages to adding such CONFIG_NUMA Kconfig
> variants for locking primitives:
>
> - an doubling of the test matrix
>
> - an doubling of the review matrix and a halving of effective review
> capacity: we've just about go the capacity to review and validate
> patches like this. Splitting out a 'only NUMA cares' variant is a
> non-starter really.
>
> - but most importantly, there's absolutely no reason to not be fast
> on 128 CPU systems in the low contended case either! Sacrificing
> the low contended case with 'on 128 CPU systems it is the contended
> path that matters' is an idiotic argument.
>
> Essentially the only area were we allow Kconfig dependencies are
> unyielding physical forces: such as lots of CPUs needing a wider CPU
> mask.
>
> As Peter said it, the right solution is to fix the contended case. If
> that also happens to speed up or better organize the uncondended code
> then that's good, but it should not make it worse.
>
> Thanks,
>
> Ingo
You are right. I am trying to measure the performance impact of MCS
queuing has on a lightly contended system. I need to write some custom
test code to get that information. With that information, I may be able
to tune it to perform more or less on par with ticket lock.
As for the additional cache line access of the MCS lock, I don't think
it is really an issued as the MCS node is allocated on local stack which
is likely to be in the cache anyway. I will report back when I have more
data.
-Longman
prev parent reply other threads:[~2014-02-06 3:09 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-24 4:28 [PATCH v11 0/4] Introducing a queue read/write lock implementation Waiman Long
2014-01-24 4:28 ` [PATCH v11 1/4] qrwlock: A " Waiman Long
2014-01-24 8:25 ` Peter Zijlstra
2014-01-25 4:39 ` Waiman Long
2014-01-24 4:28 ` [PATCH v11 2/4] qrwlock, x86: Enable x86 to use queue read/write lock Waiman Long
2014-01-24 4:28 ` [PATCH v11 3/4] qrwlock, x86: Add char and short as atomic data type in x86 Waiman Long
2014-01-24 4:28 ` [PATCH v11 4/4] qrwlock: Use the mcs_spinlock helper functions for MCS queuing Waiman Long
2014-01-24 8:26 ` Peter Zijlstra
2014-01-25 4:30 ` Waiman Long
2014-01-30 13:04 ` [PATCH v11 0/4] Introducing a queue read/write lock implementation Peter Zijlstra
2014-01-30 15:17 ` Peter Zijlstra
2014-01-30 15:43 ` Waiman Long
2014-01-30 15:50 ` Waiman Long
2014-01-30 15:53 ` Peter Zijlstra
2014-01-30 15:44 ` Peter Zijlstra
2014-01-30 17:52 ` Will Deacon
2014-01-30 18:05 ` Peter Zijlstra
2014-01-30 18:11 ` Will Deacon
2014-01-30 18:16 ` Peter Zijlstra
2014-01-31 9:26 ` Peter Zijlstra
2014-01-31 10:03 ` George Spelvin
2014-01-31 10:17 ` Peter Zijlstra
2014-01-31 11:30 ` Peter Zijlstra
2014-02-01 23:22 ` Paul E. McKenney
2014-01-31 18:59 ` Waiman Long
2014-01-31 19:47 ` Peter Zijlstra
2014-02-01 10:38 ` George Spelvin
2014-01-31 20:14 ` Peter Zijlstra
2014-01-31 21:09 ` Waiman Long
2014-02-01 1:29 ` Davidlohr Bueso
2014-02-02 9:03 ` Ingo Molnar
2014-02-03 11:38 ` Peter Zijlstra
2014-02-06 3:08 ` Waiman Long [this message]
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