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SubjectRe: [(RT RFC) PATCH v2 7/9] adaptive mutexes
Hi!

> From: Peter W.Morreale <pmorreale@novell.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@novell.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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