linux-kernel - Re: [PATCH -v4 4/5] x86,smp: keep spinlock delay values per hashed spinlock address

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Message-ID: <CANN689F=hsL0tkvhWUry9WxF3YwYV40JKiZ9ZoOQwEuLXz_iVA@mail.gmail.com>
Date:	Sat, 9 Feb 2013 15:50:37 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	linux-kernel@...r.kernel.org, aquini@...hat.com,
	eric.dumazet@...il.com, lwoodman@...hat.com, knoel@...hat.com,
	chegu_vinod@...com, raghavendra.kt@...ux.vnet.ibm.com,
	mingo@...hat.com
Subject: Re: [PATCH -v4 4/5] x86,smp: keep spinlock delay values per hashed
 spinlock address

On Wed, Feb 6, 2013 at 12:10 PM, Rik van Riel <riel@...hat.com> wrote:
> On 01/27/2013 08:04 AM, Michel Lespinasse wrote:
>>
>> On Fri, Jan 25, 2013 at 11:18 AM, Rik van Riel <riel@...hat.com> wrote:
>>>
>>> +       u32 delay = (ent->hash == hash) ? ent->delay :
>>> MIN_SPINLOCK_DELAY;
>>
>> I still don't like the reseting of delay to MIN_SPINLOCK_DELAY when
>> there is a hash collision.
>
> I've been spending some time looking at this, because I am
> not a fan either.
>
> However, it seems to work and I failed to come up with
> anything better. Therefore, I have left it as is in the
> -v5 patch series.

Does that mean you know of workloads that would regress if you didn't
reset the delay to MIN_SPINLOCK_DELAY when detecting a hash collision
?

I have not seen any public reports of that...

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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