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From: Rik van Riel <riel@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	"Vinod, Chegu" <chegu_vinod@hp.com>,
	"Low, Jason" <jason.low2@hp.com>,
	linux-tip-commits@vger.kernel.org,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	aquini@redhat.com, Michel Lespinasse <walken@google.com>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock out of line
Date: Wed, 27 Feb 2013 21:58:56 -0500	[thread overview]
Message-ID: <512EC7F0.60103@redhat.com> (raw)
In-Reply-To: <CA+55aFwa0EjGG2NUDYVLVBmXJa2k81YiuNO2yggk=GLRQxhhUQ@mail.gmail.com>

On 02/27/2013 05:13 PM, Linus Torvalds wrote:
>
> On Feb 27, 2013 1:56 PM, "Rik van Riel" <riel@redhat.com
> <mailto:riel@redhat.com>> wrote:
>>
>> No argument there, but that does in no way negate the need for some
>> performance robustness.
>
> The very numbers you posted showed that the backoff was *not* more
> robust. Quite the reverse, there was arguably more variability.

On the other hand, both MCS and the fast queue locks
implemented by Michel showed low variability and high
performance.

http://thread.gmane.org/gmane.linux.kernel/1427417

> So I really don't like how you make these sweeping statements
> *again*. Numbers talk, bullshit walks.

If you read all the text in my last mail, you will see the
link to Michel's performance results. The numbers speak for
themselves.

> The fact is, life is complicated. The simple spinlocks tend to work
> really well. People have tried fancy things before, and it turns out
> it's not as simple as they think.

The numbers for both the simple spinlocks and the
spinlock backoff kind of suck. Both of these have
high variability, and both eventually fall down
under heavy load.

The numbers for Michel's MCS and fast queue lock
implementations appear to be both fast and stable.

I agree that we need numbers.

I do not agree that other locks should be dismissed
out of hand without looking at the numbers.


  parent reply	other threads:[~2013-02-28  2:54 UTC|newest]

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-02-06 20:03 [PATCH -v5 0/5] x86,smp: make ticket spinlock proportional backoff w/ auto tuning Rik van Riel
2013-02-06 20:04 ` [PATCH -v5 1/5] x86,smp: move waiting on contended ticket lock out of line Rik van Riel
2013-02-13 12:06   ` [tip:core/locking] x86/smp: Move " tip-bot for Rik van Riel
2013-02-13 16:20     ` Linus Torvalds
2013-02-13 18:30       ` Linus Torvalds
2013-02-14  0:54         ` H. Peter Anvin
2013-02-14  1:31           ` Linus Torvalds
2013-02-14  1:56             ` H. Peter Anvin
2013-02-14 10:50         ` Ingo Molnar
2013-02-14 16:10           ` Linus Torvalds
2013-02-15 15:57             ` Ingo Molnar
2013-02-15  6:48         ` Benjamin Herrenschmidt
2013-02-13 19:08       ` Rik van Riel
2013-02-13 19:36         ` Linus Torvalds
2013-02-13 22:21           ` Rik van Riel
2013-02-13 22:40             ` Linus Torvalds
2013-02-13 23:41               ` Rik van Riel
2013-02-14  1:21                 ` Linus Torvalds
2013-02-14  1:46                   ` Linus Torvalds
2013-02-14 10:43                   ` Ingo Molnar
2013-02-27 16:42                   ` Rik van Riel
2013-02-27 17:10                     ` Linus Torvalds
2013-02-27 19:53                       ` Rik van Riel
2013-02-27 20:18                         ` Linus Torvalds
2013-02-27 21:55                           ` Rik van Riel
     [not found]                             ` <CA+55aFwa0EjGG2NUDYVLVBmXJa2k81YiuNO2yggk=GLRQxhhUQ@mail.gmail.com>
2013-02-28  2:58                               ` Rik van Riel [this message]
2013-02-28  3:19                                 ` Linus Torvalds
2013-02-28  4:06                                 ` Davidlohr Bueso
2013-02-28  4:49                                   ` Linus Torvalds
2013-02-28 15:13                                     ` Rik van Riel
2013-02-28 18:22                                       ` Linus Torvalds
2013-02-28 20:26                                         ` Linus Torvalds
2013-02-28 21:14                                           ` Rik van Riel
2013-02-28 21:58                                             ` Linus Torvalds
2013-02-28 22:38                                               ` Rik van Riel
2013-02-28 23:09                                                 ` Linus Torvalds
2013-03-01  6:42                                                   ` Rik van Riel
2013-03-01 18:18                                                     ` Davidlohr Bueso
2013-03-01 18:50                                                       ` Rik van Riel
2013-03-01 18:52                                                       ` Linus Torvalds
2013-02-06 20:04 ` [PATCH -v5 2/5] x86,smp: proportional backoff for ticket spinlocks Rik van Riel
2013-02-13 12:07   ` [tip:core/locking] x86/smp: Implement " tip-bot for Rik van Riel
2013-02-06 20:05 ` [PATCH -v5 3/5] x86,smp: auto tune spinlock backoff delay factor Rik van Riel
2013-02-13 12:08   ` [tip:core/locking] x86/smp: Auto " tip-bot for Rik van Riel
2013-02-06 20:06 ` [PATCH -v5 4/5] x86,smp: keep spinlock delay values per hashed spinlock address Rik van Riel
2013-02-13 12:09   ` [tip:core/locking] x86/smp: Keep " tip-bot for Eric Dumazet
2013-02-06 20:07 ` [PATCH -v5 5/5] x86,smp: limit spinlock delay on virtual machines Rik van Riel
2013-02-07 11:11   ` Ingo Molnar
2013-02-07 21:24     ` [PATCH fix " Rik van Riel
2013-02-13 12:10       ` [tip:core/locking] x86/smp: Limit " tip-bot for Rik van Riel
2013-02-07 11:25   ` [PATCH -v5 5/5] x86,smp: limit " Stefano Stabellini
2013-02-07 11:59     ` Raghavendra K T
2013-02-07 13:28     ` Rik van Riel
2013-02-06 20:08 ` [PATCH -v5 6/5] x86,smp: add debugging code to track spinlock delay value Rik van Riel

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