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From: Peter Maydell <peter.maydell@linaro.org>
To: qemu-devel@nongnu.org
Subject: [PULL 26/26] arm/kvm: Enable support for
KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZE
Date: Fri, 8 Sep 2023 18:05:57 +0100
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From: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
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.
Reviewed-by: Gavin Shan <gshan@redhat.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Message-id: 20230905091246.1931-1-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
include/sysemu/kvm_int.h | 1 +
accel/kvm/kvm-all.c | 1 +
target/arm/kvm.c | 61 ++++++++++++++++++++++++++++++++++++++++
qemu-options.hx | 15 ++++++++++
4 files changed, 78 insertions(+)
diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index 511b42bde5c..a5b9122cb82 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/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 2ba7521695e..ff1578bb32b 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 =3D 0;
s->kvm_dirty_ring_with_bitmap =3D false;
+ s->kvm_eager_split_size =3D 0;
s->notify_vmexit =3D NOTIFY_VMEXIT_OPTION_RUN;
s->notify_window =3D 0;
s->xen_version =3D 0;
diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index 23aeb099490..b66b936a958 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"
=20
const KVMCapabilityInfo kvm_arch_required_capabilities[] =3D {
@@ -287,6 +288,26 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
}
}
=20
+ if (s->kvm_eager_split_size) {
+ uint32_t sizes;
+
+ sizes =3D kvm_vm_check_extension(s, KVM_CAP_ARM_SUPPORTED_BLOCK_SI=
ZES);
+ if (!sizes) {
+ s->kvm_eager_split_size =3D 0;
+ warn_report("Eager Page Split support not available");
+ } else if (!(s->kvm_eager_split_size & sizes)) {
+ error_report("Eager Page Split requested chunk size not valid"=
);
+ ret =3D -EINVAL;
+ } else {
+ ret =3D kvm_vm_enable_cap(s, KVM_CAP_ARM_EAGER_SPLIT_CHUNK_SIZ=
E, 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);
=20
return ret;
@@ -1069,6 +1090,46 @@ bool kvm_arch_cpu_check_are_resettable(void)
return true;
}
=20
+static void kvm_arch_get_eager_split_size(Object *obj, Visitor *v,
+ const char *name, void *opaque,
+ Error **errp)
+{
+ KVMState *s =3D KVM_STATE(obj);
+ uint64_t value =3D 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 =3D KVM_STATE(obj);
+ uint64_t value;
+
+ if (s->fd !=3D -1) {
+ error_setg(errp, "Unable to set early-split-size after KVM has bee=
n 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 =3D 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)=
");
}
diff --git a/qemu-options.hx b/qemu-options.hx
index 463f520c57c..93d106aa9cb 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -186,6 +186,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel,
" split-wx=3Don|off (enable TCG split w^x mapping)\n"
" tb-size=3Dn (TCG translation block cache size)\n"
" dirty-ring-size=3Dn (KVM dirty ring GFN count, defaul=
t 0)\n"
+ " eager-split-size=3Dn (KVM Eager Page Split chunk size=
, default 0, disabled. ARM only)\n"
" notify-vmexit=3Drun|internal-error|disable,notify-win=
dow=3Dn (enable notify VM exit and set notify window, x86 only)\n"
" thread=3Dsingle|multi (enable multi-threaded TCG)\n",=
QEMU_ARCH_ALL)
SRST
@@ -244,6 +245,20 @@ SRST
is disabled (dirty-ring-size=3D0). When enabled, KVM will instead
record dirty pages in a bitmap.
=20
+ ``eager-split-size=3Dn``
+ 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-pa=
ge
+ 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 pag=
es
+ 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=3D0).
+
``notify-vmexit=3Drun|internal-error|disable,notify-window=3Dn``
Enables or disables notify VM exit support on x86 host and specify
the corresponding notify window to trigger the VM exit if enabled.
--=20
2.34.1