linux-kernel - Re: [(RT RFC) PATCH v2 7/9] adaptive mutexes

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Message-ID: <20080225220950.GI2659@elf.ucw.cz>
Date:	Mon, 25 Feb 2008 23:09:50 +0100
From:	Pavel Machek <pavel@....cz>
To:	Gregory Haskins <ghaskins@...ell.com>
Cc:	mingo@...e.hu, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	rostedt@...dmis.org, linux-rt-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, bill.huey@...il.com,
	kevin@...man.org, cminyard@...sta.com, dsingleton@...sta.com,
	dwalker@...sta.com, npiggin@...e.de, dsaxena@...xity.net,
	ak@...e.de, acme@...hat.com, gregkh@...e.de, sdietrich@...ell.com,
	pmorreale@...ell.com, mkohari@...ell.com
Subject: Re: [(RT RFC) PATCH v2 7/9] adaptive mutexes

Hi!

> From: Peter W.Morreale <pmorreale@...ell.com>
> 
> This patch adds the adaptive spin lock busywait to rtmutexes.  It adds
> a new tunable: rtmutex_timeout, which is the companion to the
> rtlock_timeout tunable.
> 
> Signed-off-by: Peter W. Morreale <pmorreale@...ell.com>

Not signed off by you?

> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt
> index ac1cbad..864bf14 100644
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -214,6 +214,43 @@ config RTLOCK_DELAY
>  	 tunable at runtime via a sysctl.  A setting of 0 (zero) disables
>  	 the adaptive algorithm entirely.
>  
> +config ADAPTIVE_RTMUTEX
> +        bool "Adaptive real-time mutexes"
> +        default y
> +        depends on ADAPTIVE_RTLOCK
> +        help
> +         This option adds the adaptive rtlock spin/sleep algorithm to
> +         rtmutexes.  In rtlocks, a significant gain in throughput
> +         can be seen by allowing rtlocks to spin for a distinct
> +         amount of time prior to going to sleep for deadlock avoidence.
> + 
> +         Typically, mutexes are used when a critical section may need to
> +         sleep due to a blocking operation.  In the event the critical 
> +	 section does not need to sleep, an additional gain in throughput 
> +	 can be seen by avoiding the extra overhead of sleeping.

Watch the whitespace. ... and do we need yet another config options?

> +config RTMUTEX_DELAY
> +        int "Default delay (in loops) for adaptive mutexes"
> +        range 0 10000000
> +        depends on ADAPTIVE_RTMUTEX
> +        default "3000"
> +        help
> +         This allows you to specify the maximum delay a task will use
> +	 to wait for a rt mutex before going to sleep.  Note that that
> +	 although the delay is implemented as a preemptable loop, tasks
> +	 of like priority cannot preempt each other and this setting can
> +	 result in increased latencies.
> +	 
> +         The value is tunable at runtime via a sysctl.  A setting of 0
> +	 (zero) disables the adaptive algorithm entirely.

Ouch.

> +#ifdef CONFIG_ADAPTIVE_RTMUTEX
> +
> +#define mutex_adaptive_wait         adaptive_wait
> +#define mutex_prepare_adaptive_wait prepare_adaptive_wait
> +
> +extern int rtmutex_timeout;
> +
> +#define DECLARE_ADAPTIVE_MUTEX_WAITER(name) \
> +     struct adaptive_waiter name = { .owner = NULL,               \
> +                                     .timeout = rtmutex_timeout, }
> +
> +#else
> +
> +#define DECLARE_ADAPTIVE_MUTEX_WAITER(name)
> +
> +#define mutex_adaptive_wait(lock, intr, waiter, busy) 1
> +#define mutex_prepare_adaptive_wait(lock, busy) {}

More evil macros. Macro does not behave like a function, make it
inline function if you are replacing a function.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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