Messages in this thread | | | Date | Thu, 9 Oct 2014 19:32:59 +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 07:28:34PM +0200, Peter Zijlstra wrote: > 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.
Also, if you make that preempt_count_save(), to mirror the restore, you can both preserve PREEMPT_NEED_RESCHED and avoid emitting code on !x86.
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