On 07/11/2012 02:18 PM, Christian Borntraeger wrote: > On 11/07/12 13:04, Avi Kivity wrote: >> On 07/11/2012 01:17 PM, Christian Borntraeger wrote: >>> On 11/07/12 11:06, Avi Kivity wrote: >>> [...] >>>>> Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though. >>>> >>>> Perhaps x86 should copy this. >>> >>> See arch/s390/lib/spinlock.c >>> The basic idea is using several heuristics: >>> - loop for a given amount of loops >>> - check if the lock holder is currently scheduled by the hypervisor >>> (smp_vcpu_scheduled, which uses the sigp sense running instruction) >>> Dont know if such thing is available for x86. It must be a lot cheaper >>> than a guest exit to be useful >> >> We could make it available via shared memory, updated using preempt >> notifiers. Of course piling on more pv makes this less attractive. >> >>> - if lock holder is not running and we looped for a while do a directed >>> yield to that cpu. >>> >>>> >>>>> So there is no win here, but there are other cases were diag44 is used, e.g. cpu_relax. >>>>> I have to double check with others, if these cases are critical, but for now, it seems >>>>> that your dummy implementation for s390 is just fine. After all it is a no-op until >>>>> we implement something. >>>> >>>> Does the data structure make sense for you? If so we can move it to >>>> common code (and manage it in kvm_vcpu_on_spin()). We can guard it with >>>> CONFIG_KVM_HAVE_CPU_RELAX_INTERCEPT or something, so other archs don't >>>> have to pay anything. >>> >>> Ignoring the name, >> >> What name would you suggest? > > maybe vcpu_no_progress instead of pause_loop_exited Ah, I thouht you objected to the CONFIG var. Maybe call it cpu_relax_intercepted since that's the linuxy name for the instruction. -- error compiling committee.c: too many arguments to function -- 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
