KVM: s390: Changes for 4.10 (via kvm/next)
Two small optimizations to not do register reloading in
vcpu_put/get, instead do it in the ioctl path. This reduces
the overhead for schedule-intense workload that does not
exit to QEMU. (e.g. KVM guest with eventfd/irqfd that
does a lot of context switching with vhost or iothreads).
KVM: s390: handle floating point registers in the run ioctl not in vcpu_put/load
Right now we switch the host fprs/vrs in kvm_arch_vcpu_load and switch
back in kvm_arch_vcpu_put. This process is already optimized
since commit 9977e886cbbc7 ("s390/kernel: lazy restore fpu registers")
avoiding double save/restores on schedule. We still reload the pointers
and test the guest fpc on each context switch, though.
We can minimize the cost of vcpu_load/put by doing the test in the
VCPU_RUN ioctl itself. As most VCPU threads almost never exit to
userspace in the common fast path, this allows to avoid this overhead
for the common case (eventfd driven I/O, all exits including sleep
handled in the kernel) - making kvm_arch_vcpu_load/put basically
disappear in perf top.
Also adapt the fpu get/set ioctls.
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
1 file changed
