linux-kernel - Re: [RFC PATCH 0/5] x86,smp: make ticket spinlock proportional backoff w/ auto tuning

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Message-ID: <CANN689GPzjJW7OiYhFJi1xLSN+606auMeJCsxR_CHL_T4aETZg@mail.gmail.com>
Date:	Thu, 3 Jan 2013 02:46:01 -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, jeremy@...p.org,
	Jan Beulich <JBeulich@...ell.com>,
	Thomas Gleixner <tglx@...utronix.de>, knoel@...hat.com
Subject: Re: [RFC PATCH 0/5] x86,smp: make ticket spinlock proportional
 backoff w/ auto tuning

On Wed, Jan 2, 2013 at 9:15 PM, Rik van Riel <riel@...hat.com> wrote:
> The v2 series integrates several ideas from Michel Lespinasse
> and Eric Dumazet, which should result in better throughput and
> nicer behaviour in situations with contention on multiple locks.
>
> Please let me know if you manage to break this code in any way,
> so I can fix it...

I'm seeing some very weird things on my 3 test machines. Looks like
the spinlock delay sometimes gets crazy, at which point spinlock
performance becomes unbearable and the network driver freaks out.

# ./spinlock_load_test
 1 spinlocks: 24159990
 2 spinlocks: 12900657
 3 spinlocks: 11547771
 4 spinlocks: 9113
 6 spinlocks: 259
 8 spinlocks: 310
12 spinlocks: 283
16 spinlocks:
<seems to be stuck here; meanwhile my serial console fills up with
network driver cries>

Well, I take it as an incitation to pay special attention to this code review :)

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