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Re: [PATCH RFC 8/9] KVM: Add dirty-ring-size property
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [PATCH RFC 8/9] KVM: Add dirty-ring-size property |
Date: |
Wed, 25 Mar 2020 20:00:31 +0000 |
User-agent: |
Mutt/1.13.3 (2020-01-12) |
* Peter Xu (address@hidden) wrote:
> Add a parameter for size of dirty ring. If zero, dirty ring is
> disabled. Otherwise dirty ring will be enabled with the per-vcpu size
> as specified. If dirty ring cannot be enabled due to unsupported
> kernel, it'll fallback to dirty logging. By default, dirty ring is
> not enabled (dirty-ring-size==0).
>
> Signed-off-by: Peter Xu <address@hidden>
> ---
> accel/kvm/kvm-all.c | 64 +++++++++++++++++++++++++++++++++++++++++++++
> qemu-options.hx | 3 +++
> 2 files changed, 67 insertions(+)
>
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index ea7b8f7ca5..6d145a8b98 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -127,6 +127,8 @@ struct KVMState
> KVMMemoryListener *ml;
> AddressSpace *as;
> } *as;
> + int kvm_dirty_ring_size;
> + int kvm_dirty_gfn_count; /* If nonzero, then kvm dirty ring enabled */
> };
>
> KVMState *kvm_state;
> @@ -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?
> + }
> + }
> +
> kvm_memory_listener_register(s, &s->memory_listener,
> &address_space_memory, 0);
> memory_listener_register(&kvm_io_listener,
> @@ -3037,6 +3066,33 @@ bool kvm_kernel_irqchip_split(void)
> return kvm_state->kernel_irqchip_split == ON_OFF_AUTO_ON;
> }
>
> +static void kvm_get_dirty_ring_size(Object *obj, Visitor *v,
> + const char *name, void *opaque,
> + Error **errp)
> +{
> + KVMState *s = KVM_STATE(obj);
> + int64_t value = s->kvm_dirty_ring_size;
> +
> + visit_type_int(v, name, &value, errp);
> +}
> +
> +static void kvm_set_dirty_ring_size(Object *obj, Visitor *v,
> + const char *name, void *opaque,
> + Error **errp)
> +{
> + KVMState *s = KVM_STATE(obj);
> + Error *error = NULL;
> + int64_t value;
> +
> + visit_type_int(v, name, &value, &error);
> + if (error) {
> + error_propagate(errp, error);
> + return;
> + }
> +
> + s->kvm_dirty_ring_size = value;
> +}
> +
> static void kvm_accel_instance_init(Object *obj)
> {
> KVMState *s = KVM_STATE(obj);
> @@ -3044,6 +3100,8 @@ static void kvm_accel_instance_init(Object *obj)
> s->kvm_shadow_mem = -1;
> s->kernel_irqchip_allowed = true;
> s->kernel_irqchip_split = ON_OFF_AUTO_AUTO;
> + /* By default off */
> + s->kvm_dirty_ring_size = 0;
> }
>
> static void kvm_accel_class_init(ObjectClass *oc, void *data)
> @@ -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.
> + 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.
Dave
> @item thread=single|multi
> Controls number of TCG threads. When the TCG is multi-threaded there will be
> one
> thread per vCPU therefor taking advantage of additional host cores. The
> default
> --
> 2.24.1
>
>
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- Re: [PATCH RFC 8/9] KVM: Add dirty-ring-size property,
Dr. David Alan Gilbert <=