On 10/09, Peter Zijlstra wrote: > > 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: > > > @@ -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.
No, it must not be set. It was cleared by clear_preempt_need_resched() in __schedule(), and nobody can set it. (schedule_tail() also relies on fact it runs with irqs disabled). But, > Also, if you make that preempt_count_save(), to mirror the restore, Yes, agreed. That is why I said we probably want preempt_count_raw() (or _save). This way we avoid the unnecessary "&= ~PREEMPT_NEED_RESCHED" on x86. > can both preserve PREEMPT_NEED_RESCHED and avoid emitting code on !x86. This too, although gcc should optimize this code out anyway. At least it seems to do on x86 if I make preempt_count_restore() empty. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
