On 22/12/11 13:35, Avi Kivity wrote: > On 12/22/2011 01:56 PM, Christian Borntraeger wrote: >> Avi, Marcelo, >> >> currently userspace can access guest registers via several ioctls. Some >> of these registers might be useful very often. Here the system call overhead >> for ioctl can make an exit more expensive than necessary. >> In a discussion with Alex Graf we concluded that it might be beneficial to >> have a subset of registers available in kvm_run. (The ioctls will also be >> available). >> >> This series provides a prototype implementation together with two example >> users for s390. >> >> > > Interesting. Other archs emulate everything to do with registers in the > kernel, so this is not a fast path. > > What workload does this benefit? My main concern was the prefix register (this is a per cpu register that defines the address of two pages that are swapped with the pages at 0 for this cpu). SMP on s390 is done that way (e.g. interrupt things are stored in page 0 for this cpu) The storage that qemu sees is storage without prefix. For architecture compliance we actually must check _every_ memory access if it hits the prefix/swpa area and the add/subtract the prefix value. I just added the ability to share other registers later after some discussions with Alexander Graf because it seems to be doable for almost no cost. 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
