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 KA0UgdNt 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reschedulable", and get rid of - or >> at least not increasingly add to - the cond_resched() mess. > Isn't that called PREEMPT=y ? That tracks precisely all the constraints > required to know when/if we can preempt. > > The whole voluntary preempt model is basically the traditional > co-operative preemption model and that fully relies on manual yields. > > The problem with the REP prefix (and Xen hypercalls) is that > they're long running instructions and it becomes fundamentally > impossible to put a cond_resched() in. Any VMM - Xen isn't special here. And if we're talking about instructions, then CPUID, GETSEC and ENCL{S,U} and plenty of {RD,WR}MSRs in in a similar category, being effectively blocking RPC operations to something else in the platform. The Xen evtchn upcall logic in Linux does cond_resched() when possible.  i.e. long-running hypercalls issued with interrupts enabled can reschedule if an interrupt occurs, which is pretty close to how REP works too. ~Andrew