Re: [linux-audio-dev] Re: [announce] [patch] Voluntary Kernel Preemption Patch

* Andrew Morton <akpm(a)osdl.org> wrote: i have solved the fundamental SMP latency problems in the -Q7 patch, by redesigning how SMP preemption is done. Here's the relevant changelog entry: [...] the main change in this patch are more SMP latency fixes. The stock kernel, even with CONFIG_PREEMPT enabled, didnt have any spin-nicely preemption logic for the following, commonly used SMP locking primitives: read_lock(), spin_lock_irqsave(), spin_lock_irq(), spin_lock_bh(), read_lock_irqsave(), read_lock_irq(), read_lock_bh(), write_lock_irqsave(), write_lock_irq(), write_lock_bh(). Only spin_lock() and write_lock() [the two simplest cases] where covered. In addition to the preemption latency problems, the _irq() variants in the above list didnt do any IRQ-enabling while spinning - possibly resulting in excessive irqs-off sections of code! -Q7 fixes all of these latency problems: we now re-enable interrupts while spinning in all possible cases, and a spinning op stays preemptible if this is a beginning of a new critical section. [...] feedback from Mark H Johnson: http://lkml.org/lkml/2004/8/30/202 the latest patch is: http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.9-rc1-bk4-… i'm already in the process of cleaning up the patch and making it ready for splitup & merge. The spinlock fixes will be amongst the first patches i'll send you. Ingo