From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Waiman Long <waiman.long@hp.com>,
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: Mon, 3 Feb 2014 12:38:57 +0100 [thread overview]
Message-ID: <20140203113857.GG8874@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140202090357.GA1006@gmail.com>
On Sun, Feb 02, 2014 at 10:03:57AM +0100, 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.
Not to mention distros will only ever pick one.
Also, there's probably several orders of magnitude more single and dual
socket systems out there than there are quad or bigger systems.
So even if the lightly contended case is say only 1% slower, that could
still add up to more cycles lost than won over all computers out there
running Linux.
next prev parent reply other threads:[~2014-02-03 11:39 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 [this message]
2014-02-06 3:08 ` Waiman Long
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