On Fri, 6 Apr 2007, Robert P. J. Day wrote:
> in the kernel config menu, does "Voluntary Kernel Preemption" mean
> *only* voluntary preemption, or *in addition to* the regular forced
> preemption? the help screen strongly suggests "in addition to", but
> i've been burned by bad help content before. :-P
never mind, i just RTFS and i think i have the answer. kernel.h
contains the following snippet:
==========================
#ifdef CONFIG_PREEMPT_VOLUNTARY
extern int cond_resched(void);
# define might_resched() cond_resched()
#else
# define might_resched() do { } while (0)
#endif
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
void __might_sleep(char *file, int line);
# define might_sleep() \
do { __might_sleep(__FILE__, __LINE__); might_resched(); } while (0)
#else
# define might_sleep() do { might_resched(); } while (0)
#endif
#define might_sleep_if(cond) do { if (cond) might_sleep(); } while (0)
==========================
so selecting voluntary preemption simply defines possible preemption
whenever you invoke "might_sleep()" or "might_sleep_if()", that's all.
regular (forced) preemption is, of course, still in effect.
rday
--
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA
http://fsdev.net/wiki/index.php?title=Main_Page
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