Messages in this thread | | | Date | Thu, 9 Oct 2014 19:28:34 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/2] sched: schedule_tail() should disable preemption |
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On Thu, Oct 09, 2014 at 06:57:13PM +0200, Oleg Nesterov wrote: > > Your earlier proposal would penalize every > > !x86 arch by adding extra code to the scheduler core while they already > > automagically preserve their thread_info::preempt_count. > > Sure, and it can't be even compiled on !x86. > > But this is simple, just we need a new helper, preempt_count_restore(), > defined as nop in asm-generic/preempt.h. Well, perhaps another helper > makes sense, preempt_count_raw() which simply reads the counter, but > this is minor. > > After the patch below we can remove ->saved_preempt_count. Including > init_task_preempt_count(), it is no longer needed after the change in > schedule_tail().
Ah, right, this makes more sense.
> @@ -2333,10 +2336,12 @@ context_switch(struct rq *rq, struct task_struct *prev, > #endif > > context_tracking_task_switch(prev, next); > + > + pc = preempt_count();
The only problem here is that you can loose PREEMPT_NEED_RESCHED, I haven't thought about whether that is a problem here or not.
> /* Here we just switch the register state and the stack. */ > switch_to(prev, next, prev); > - > barrier(); > + preempt_count_restore(pc); > /* > * this_rq must be evaluated again because prev may have moved > * CPUs since it called schedule(), thus the 'rq' on its stack >
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