* Lee Revell <[EMAIL PROTECTED]> wrote: > I can also add that La Monte H. P. Yarroll's patch to daemonize > softirqs seems to provide major improvements in latency (does not help > this problem of course). There has been at least one other patch > posted to LKML that that does the same thing. Will this feature be in > the kernel anytime soon?
we already 'daemonize' softirqs in the stock kernel if the load is high enough. (this is what ksoftirqd does) So the only question is a tunable to make this deferring of softirq load mandatory. Yarroll's patch is quite complex, i dont think that is necessary. It also has at least one conceptual problem, the NOP-ing of local_bh_disable/enable in case of CONFIG_SOFTIRQ_THREADS is clearly wrong. Yarroll? I've added a very simple solution to daemonize softirqs similar to Yarroll's patch to the -H5 version of voluntary-preempt: http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8-rc2-H5 the 'level' of preemption is controlled via the value of voluntary_preempt - a level of 2 (default) means that softirq-deferring is done too. A level of 1 means only the extra preemption points are activated, level 0 means the vanilla scheduling and softirq behavior. below i've also attached a softirq.c patch against 2.6.8-rc2 that does unconditional deferring. (this patch is of course not intended to be merged upstream as-is, since normally we want to process softirqs right after the irq context.) Ingo --- linux/kernel/softirq.c.orig +++ linux/kernel/softirq.c @@ -70,7 +70,7 @@ static inline void wakeup_softirqd(void) */ #define MAX_SOFTIRQ_RESTART 10 -asmlinkage void __do_softirq(void) +asmlinkage void ___do_softirq(void) { struct softirq_action *h; __u32 pending; @@ -106,6 +106,23 @@ restart: __local_bh_enable(); } +asmlinkage void __do_softirq(void) +{ + /* + * 'preempt harder'. Push all softirq processing off to ksoftirqd. + */ + if (local_softirq_pending()) + wakeup_softirqd(); +} + +asmlinkage void _do_softirq(void) +{ + local_irq_disable(); + ___do_softirq(); + local_irq_enable(); +} + + #ifndef __ARCH_HAS_DO_SOFTIRQ asmlinkage void do_softirq(void) @@ -340,7 +363,7 @@ static int ksoftirqd(void * __bind_cpu) preempt_disable(); if (cpu_is_offline((long)__bind_cpu)) goto wait_to_die; - do_softirq(); + _do_softirq(); preempt_enable(); cond_resched(); }
