Am Thursday 07 May 2009 12:19:32 schrieb Avi Kivity: > Makes sense. > > Back when irqsave/irqrestore were expensive on x86 (P4 days, I think it > was ~100 cycles) there was talk of using a software irq disable flag > instead of using the hardware support. So > > - local_irq_disable() sets a flag > > - interrupt handlers check the flag, if set they schedule the interrupt > handler and return immediately > > - local_irq_restore() clears the flag and fires and scheduled handlers > > Now these operations are pretty cheap on x86, but maybe that can apply > to s390. Interesting idea. Nevertheless, I dont think it improve our situation. The affected instructions (stosm and stnsm) are more expensive than compare and swap, but its nowhere near the ~100 cycles of P4. Christian -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
