Now that we have Eager Page Split support added for ARM in the kernel, enable it in Qemu. This adds, -eager-split-size to -accel sub-options to set the eager page split chunk size. -enable KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE. The chunk size specifies how many pages to break at a time, using a single allocation. Bigger the chunk size, more pages need to be allocated ahead of time. Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx> --- v2: https://lore.kernel.org/qemu-devel/20230815092709.1290-1-shameerali.kolothum.thodi@xxxxxxxxxx/ -Addressed comments from Gavin(Thanks). RFC v1: https://lore.kernel.org/qemu-devel/20230725150002.621-1-shameerali.kolothum.thodi@xxxxxxxxxx/ -Updated qemu-options.hx with description -Addressed review comments from Peter and Gavin(Thanks). --- accel/kvm/kvm-all.c | 1 + include/sysemu/kvm_int.h | 1 + qemu-options.hx | 15 +++++++++ target/arm/kvm.c | 68 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 85 insertions(+) diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index 2ba7521695..ff1578bb32 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -3763,6 +3763,7 @@ static void kvm_accel_instance_init(Object *obj) /* KVM dirty ring is by default off */ s->kvm_dirty_ring_size = 0; s->kvm_dirty_ring_with_bitmap = false; + s->kvm_eager_split_size = 0; s->notify_vmexit = NOTIFY_VMEXIT_OPTION_RUN; s->notify_window = 0; s->xen_version = 0; diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h index 511b42bde5..a5b9122cb8 100644 --- a/include/sysemu/kvm_int.h +++ b/include/sysemu/kvm_int.h @@ -116,6 +116,7 @@ struct KVMState uint64_t kvm_dirty_ring_bytes; /* Size of the per-vcpu dirty ring */ uint32_t kvm_dirty_ring_size; /* Number of dirty GFNs per ring */ bool kvm_dirty_ring_with_bitmap; + uint64_t kvm_eager_split_size; /* Eager Page Splitting chunk size */ struct KVMDirtyRingReaper reaper; NotifyVmexitOption notify_vmexit; uint32_t notify_window; diff --git a/qemu-options.hx b/qemu-options.hx index 29b98c3d4c..2e70704ee8 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -186,6 +186,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel, " split-wx=on|off (enable TCG split w^x mapping)\n" " tb-size=n (TCG translation block cache size)\n" " dirty-ring-size=n (KVM dirty ring GFN count, default 0)\n" + " eager-split-size=n (KVM Eager Page Split chunk size, default 0, disabled. ARM only)\n" " notify-vmexit=run|internal-error|disable,notify-window=n (enable notify VM exit and set notify window, x86 only)\n" " thread=single|multi (enable multi-threaded TCG)\n", QEMU_ARCH_ALL) SRST @@ -244,6 +245,20 @@ SRST is disabled (dirty-ring-size=0). When enabled, KVM will instead record dirty pages in a bitmap. + ``eager-split-size=n`` + KVM implements dirty page logging at the PAGE_SIZE granularity and + enabling dirty-logging on a huge-page requires breaking it into + PAGE_SIZE pages in the first place. KVM on ARM does this splitting + lazily by default. There are performance benefits in doing huge-page + split eagerly, especially in situations where TLBI costs associated + with break-before-make sequences are considerable and also if guest + workloads are read intensive. The size here specifies how many pages + to break at a time and needs to be a valid block size which is + 1GB/2MB/4KB, 32MB/16KB and 512MB/64KB for 4KB/16KB/64KB PAGE_SIZE + respectively. Be wary of specifying a higher size as it will have an + impact on the memory. By default, this feature is disabled + (eager-split-size=0). + ``notify-vmexit=run|internal-error|disable,notify-window=n`` Enables or disables notify VM exit support on x86 host and specify the corresponding notify window to trigger the VM exit if enabled. diff --git a/target/arm/kvm.c b/target/arm/kvm.c index 23aeb09949..28d81ca790 100644 --- a/target/arm/kvm.c +++ b/target/arm/kvm.c @@ -30,6 +30,7 @@ #include "exec/address-spaces.h" #include "hw/boards.h" #include "hw/irq.h" +#include "qapi/visitor.h" #include "qemu/log.h" const KVMCapabilityInfo kvm_arch_required_capabilities[] = { @@ -247,6 +248,12 @@ int kvm_arm_get_max_vm_ipa_size(MachineState *ms, bool *fixed_ipa) return ret > 0 ? ret : 40; } +static inline bool kvm_arm_eager_split_size_valid(uint64_t req_size, + uint32_t sizes) +{ + return req_size & sizes; +} + int kvm_arch_get_default_type(MachineState *ms) { bool fixed_ipa; @@ -287,6 +294,27 @@ int kvm_arch_init(MachineState *ms, KVMState *s) } } + if (s->kvm_eager_split_size) { + uint32_t sizes; + + sizes = kvm_vm_check_extension(s, KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES); + if (!sizes) { + s->kvm_eager_split_size = 0; + warn_report("Eager Page Split support not available"); + } else if (!kvm_arm_eager_split_size_valid(s->kvm_eager_split_size, + sizes)) { + error_report("Eager Page Split requested chunk size not valid"); + ret = -EINVAL; + } else { + ret = kvm_vm_enable_cap(s, KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE, 0, + s->kvm_eager_split_size); + if (ret < 0) { + error_report("Enabling of Eager Page Split failed: %s", + strerror(-ret)); + } + } + } + kvm_arm_init_debug(s); return ret; @@ -1069,6 +1097,46 @@ bool kvm_arch_cpu_check_are_resettable(void) return true; } +static void kvm_arch_get_eager_split_size(Object *obj, Visitor *v, + const char *name, void *opaque, + Error **errp) +{ + KVMState *s = KVM_STATE(obj); + uint64_t value = s->kvm_eager_split_size; + + visit_type_size(v, name, &value, errp); +} + +static void kvm_arch_set_eager_split_size(Object *obj, Visitor *v, + const char *name, void *opaque, + Error **errp) +{ + KVMState *s = KVM_STATE(obj); + uint64_t value; + + if (s->fd != -1) { + error_setg(errp, "Unable to set early-split-size after KVM has been initialized"); + return; + } + + if (!visit_type_size(v, name, &value, errp)) { + return; + } + + if (value && !is_power_of_2(value)) { + error_setg(errp, "early-split-size must be a power of two"); + return; + } + + s->kvm_eager_split_size = value; +} + void kvm_arch_accel_class_init(ObjectClass *oc) { + object_class_property_add(oc, "eager-split-size", "size", + kvm_arch_get_eager_split_size, + kvm_arch_set_eager_split_size, NULL, NULL); + + object_class_property_set_description(oc, "eager-split-size", + "Eager Page Split chunk size for hugepages. (default: 0, disabled)"); } -- 2.34.1
