* Peter Xu (pet...@redhat.com) wrote: > On Wed, Mar 25, 2020 at 08:00:31PM +0000, Dr. David Alan Gilbert wrote: > > > @@ -2077,6 +2079,33 @@ static int kvm_init(MachineState *ms) > > > s->memory_listener.listener.coalesced_io_add = > > > kvm_coalesce_mmio_region; > > > s->memory_listener.listener.coalesced_io_del = > > > kvm_uncoalesce_mmio_region; > > > > > > + /* > > > + * Enable KVM dirty ring if supported, otherwise fall back to > > > + * dirty logging mode > > > + */ > > > + if (s->kvm_dirty_ring_size > 0) { > > > + /* Read the max supported pages */ > > > + ret = kvm_vm_check_extension(kvm_state, KVM_CAP_DIRTY_LOG_RING); > > > + if (ret > 0) { > > > + if (s->kvm_dirty_ring_size > ret) { > > > + error_report("KVM dirty ring size %d too big (maximum is > > > %d). " > > > + "Please use a smaller value.", > > > + s->kvm_dirty_ring_size, ret); > > > + goto err; > > > + } > > > + > > > + ret = kvm_vm_enable_cap(s, KVM_CAP_DIRTY_LOG_RING, 0, > > > + s->kvm_dirty_ring_size); > > > + if (ret) { > > > + error_report("Enabling of KVM dirty ring failed: %d", > > > ret); > > > + goto err; > > > + } > > > + > > > + s->kvm_dirty_gfn_count = > > > + s->kvm_dirty_ring_size / sizeof(struct kvm_dirty_gfn); > > > > What happens if I was to pass dirty-ring-size=1 ? > > Then the count would be 0 and things would get upset somewhere? > > Do you need to check for a minimum postive value? > > The above kvm_vm_enable_cap() should fail directly and QEMU will stop. > Yes we should check it, but kernel will do that in all cases, so I > just didn't do that explicitly again in the userspace.
We probably should have that check since you can give them a more obvious error message. > I was planning this to be an advanced feature so the user of this > parameter should know the rules to pass values in. Advanced users just make advanced mistakes :-) I did wonder if perhaps this option should be a count of entries rather than a byte size. > Of course we can introduce another global knob to enable/disable this > feature as a whole, then I can offer a default value for the size > parameter. I just didn't bother that in this RFC version, but I can > switch to that if that's preferred. > > [...] > > > > @@ -3065,6 +3123,12 @@ static void kvm_accel_class_init(ObjectClass *oc, > > > void *data) > > > NULL, NULL, &error_abort); > > > object_class_property_set_description(oc, "kvm-shadow-mem", > > > "KVM shadow MMU size", &error_abort); > > > + > > > + object_class_property_add(oc, "dirty-ring-size", "int", > > > + kvm_get_dirty_ring_size, kvm_set_dirty_ring_size, > > > + NULL, NULL, &error_abort); > > > > I don't think someone passing in a non-number should cause an abort; > > it should exit, but I don't think it should abort/core. > > It won't - &error_abort is for the operation to add the property. It > should never fail. > > User illegal input will look like this (a graceful exit): > > $ ./x86_64-softmmu/qemu-system-x86_64 -accel kvm,dirty-ring-size=a > qemu-system-x86_64: -accel kvm,dirty-ring-size=a: Parameter 'dirty-ring-size' > expects int64 OK good. > > > > > + object_class_property_set_description(oc, "dirty-ring-size", > > > + "KVM dirty ring size (<=0 to disable)", &error_abort); > > > } > > > > > > static const TypeInfo kvm_accel_type = { > > > diff --git a/qemu-options.hx b/qemu-options.hx > > > index 224a8e8712..140bd38726 100644 > > > --- a/qemu-options.hx > > > +++ b/qemu-options.hx > > > @@ -119,6 +119,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel, > > > " kernel-irqchip=on|off|split controls accelerated > > > irqchip support (default=on)\n" > > > " kvm-shadow-mem=size of KVM shadow MMU in bytes\n" > > > " tb-size=n (TCG translation block cache size)\n" > > > + " dirty-ring-size=n (KVM dirty ring size in Bytes)\n" > > > " thread=single|multi (enable multi-threaded TCG)\n", > > > QEMU_ARCH_ALL) > > > STEXI > > > @item -accel @var{name}[,prop=@var{value}[,...]] > > > @@ -140,6 +141,8 @@ irqchip completely is not recommended except for > > > debugging purposes. > > > Defines the size of the KVM shadow MMU. > > > @item tb-size=@var{n} > > > Controls the size (in MiB) of the TCG translation block cache. > > > +@item dirty-ring-size=@val{n} > > > +Controls the size (in Bytes) of KVM dirty ring (<=0 to disable). > > > > I don't see the point in allowing < 0 ; I'd ban it. > > Sure; I can switch to an uint64. Great. Dave > Thanks, > > -- > Peter Xu > -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK