Hi Mohammed, On Thu, 2009-08-13 at 15:59 +0300, Mohammed Gamal wrote: > Hi All, > I know that kernel preemption exists in order to allow high-priority > processes to interrupt the kernel if the kernel executes on relatively > long code paths in order to improve latency times and process > responsiveness. However, I am curious to know when and where the > kernel gets preempted and at what code paths. I searched LXR for > instances where preempt_schedule() gets called for instance but it > seems it never gets explicitly called anywhere in the kernel (please > CCIW). So, when exactly does the kernel get preempted? A pointer to > the actual code path where that happens is appreciated. > > Regards, > Mohammed > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ > Because I had the indexer/search from Eclipse on into my embedded target kernel anyway, I did a quick scan for "preempt_schedule". With 2.6.29.4 kernel I get 35 matches : - 4 in system.map - 1 in module.symvers - 3 in sched.c Line 4681 : asmlinkage void __sched preempt_schedule(void) Line 4712 : asmlinkage void __sched preempt_schedule_irq(void) and just the exported symbol - 2 in kprobes.c the only relevant is : static struct kprobe_blackpoint kprobe_blacklist[] = { {"preempt_schedule",}, {NULL} /* Terminator */ - 2 in preempt.h the relevant is macro : #define preempt_check_resched() \ do { \ if (unlikely(test_thread_flag(TIF_NEED_RESCHED))) \ preempt_schedule(); \ } while (0) - 2 in Documentation /ftrace.txt Line 811 & 1043 - one for each entry in /arch/* .. eg. in arch/arm/kernel/entry-armv.S : #ifdef CONFIG_PREEMPT svc_preempt: mov r8, lr 1: bl preempt_schedule_irq @ irq en/disable is done inside ldr r0, [tsk, #TI_FLAGS] @ get new tasks TI_FLAGS tst r0, #_TIF_NEED_RESCHED moveq pc, r8 @ go again b 1b #endif Perhaps that'll give a hand. HTH -- Best regards, Kris -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
