linux-kernel - Re: [RFC PATCH 3/3 -v2] x86,smp: auto tune spinlock backoff delay factor

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Message-ID: <50DC9CE1.9030709@redhat.com>
Date:	Thu, 27 Dec 2012 14:09:21 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Jan Beulich <jbeulich@...e.com>
CC:	eric.dumazet@...il.com, rostedt@...dmis.org, therbert@...gle.com,
	walken@...gle.com, jeremy@...p.org, tglx@...utronix.de,
	aquini@...hat.com, lwoodman@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 3/3 -v2] x86,smp: auto tune spinlock backoff delay
 factor

On 12/27/2012 01:41 PM, Jan Beulich wrote:
>>>> Rik van Riel <riel@...hat.com> 12/27/12 4:01 PM >>>
>> On 12/27/2012 09:27 AM, Eric Dumazet wrote:
>>> So the hash sounds good to me, because the hash key could mix both lock
>>> address and caller IP ( __builtin_return_address(1) in
>>> ticket_spin_lock_wait())
>>
>> The lock acquisition time depends on the holder of the lock,
>> and what the CPUs ahead of us in line will do with the lock,
>> not on the caller IP of the spinner.
>
> The lock holder could supply its __builtin_return_address(0) for use
> in eventual hashing.
>
> Also, with all of this - did you evaluate the alternative of using
> monitor/mwait instead?

How much bus traffic do monitor/mwait cause behind the scenes?

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