• Ingo Molnar's avatar
    [PATCH] sched: voluntary kernel preemption · f8cbd99b
    Ingo Molnar authored
    This patch adds a new preemption model: 'Voluntary Kernel Preemption'.  The
    3 models can be selected from a new menu:
    
                (X) No Forced Preemption (Server)
                ( ) Voluntary Kernel Preemption (Desktop)
                ( ) Preemptible Kernel (Low-Latency Desktop)
    
    we still default to the stock (Server) preemption model.
    
    Voluntary preemption works by adding a cond_resched()
    (reschedule-if-needed) call to every might_sleep() check.  It is lighter
    than CONFIG_PREEMPT - at the cost of not having as tight latencies.  It
    represents a different latency/complexity/overhead tradeoff.
    
    It has no runtime impact at all if disabled.  Here are size stats that show
    how the various preemption models impact the kernel's size:
    
        text    data     bss     dec     hex filename
     3618774  547184  179896 4345854  424ffe vmlinux.stock
     3626406  547184  179896 4353486  426dce vmlinux.voluntary   +0.2%
     3748414  548640  179896 4476950  445016 vmlinux.preempt     +3.5%
    
    voluntary-preempt is +0.2% of .text, preempt is +3.5%.
    
    This feature has been tested for many months by lots of people (and it's
    also included in the RHEL4 distribution and earlier variants were in Fedora
    as well), and it's intended for users and distributions who dont want to
    use full-blown CONFIG_PREEMPT for one reason or another.
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    f8cbd99b
Kconfig.preempt 2.27 KB