On 15/09/2015 18:13, Cornelia Huck wrote: > On Tue, 15 Sep 2015 17:07:55 +0200 > Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > >> On 15/09/2015 08:41, Jason Wang wrote: >>> +With KVM_CAP_FAST_MMIO, a zero length mmio eventfd is allowed for >>> +kernel to ignore the length of guest write and get a possible faster >>> +response. Note the speedup may only work on some specific >>> +architectures and setups. Otherwise, it's as fast as wildcard mmio >>> +eventfd. >> >> I don't really like tying the capability to MMIO, especially since >> zero length ioeventfd is already accepted for virtio-ccw. > > Actually, zero length ioeventfd does not make sense for virtio-ccw; Can you explain why? If there is any non-zero valid length, "wildcard length" (represented by zero) would also make sense. Paolo > we just don't check it (although we probably should). > >> >> What about the following? >> >> diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt >> index 7a3cb48a644d..247944071cc8 100644 >> --- a/Documentation/virtual/kvm/api.txt >> +++ b/Documentation/virtual/kvm/api.txt >> @@ -1627,11 +1627,10 @@ to the registered address is equal to datamatch in struct kvm_ioeventfd. >> For virtio-ccw devices, addr contains the subchannel id and datamatch the >> virtqueue index. >> >> -With KVM_CAP_FAST_MMIO, a zero length mmio eventfd is allowed for >> -kernel to ignore the length of guest write and get a possible faster >> -response. Note the speedup may only work on some specific >> -architectures and setups. Otherwise, it's as fast as wildcard mmio >> -eventfd. >> +With KVM_CAP_IOEVENTFD_ANY_LENGTH, a zero length ioeventfd is allowed, and >> +the kernel will ignore the length of guest write and get a faster vmexit. > > s/get/may get/ ? > >> +The speedup may only apply to specific architectures, but the ioeventfd will >> +work anyway. > -- 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
