Original description of a patch by Alexander Graf that did
something similar:
Commit f010bc643a (target-i386: add feature kvm_pv_unhalt) introduced the
kvm_pv_unhalt feature but didn't enable it by default.
Without kvm_pv_unhalt we see a measurable degradation in scheduling
performance, so enabling it by default does make sense IMHO. This patch
just flips it to default to on by default.
[With kvm_pv_unhalt disabled]
$ perf bench sched messaging -l 10000
Total time: 8.573 [sec]
[With kvm_pv_unhalt enabled]
$ perf bench sched messaging -l 10000
Total time: 4.416 [sec]
This patch does the same as that patch, but using a
kvm_auto_enable_pv_unhalt flag to keep compatibility on older
machine-types.
kvm_pv_unhalt support was added to Linux on v3.12 (Linux commit
6aef266c6e17b798a1740cf70cd34f90664740b3), so update the system
requirements section in qemu-doc.texi accordingly.
Suggested-by: Alexander Graf <[email protected]>
Cc: Alexander Graf <[email protected]>
Signed-off-by: Eduardo Habkost <[email protected]>
---
include/hw/i386/pc.h | 4 ++++
target/i386/cpu.h | 3 +++
target/i386/cpu.c | 7 +++++++
qemu-doc.texi | 2 +-
4 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index d2742dd0bc..19b42de224 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -375,6 +375,10 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
.driver = TYPE_X86_CPU,\
.property = "x-hv-max-vps",\
.value = "0x40",\
+ },{\
+ .driver = TYPE_X86_CPU,\
+ .property = "x-kvm-auto-enable-pv-unhalt",\
+ .value = "off",\
},
#define PC_COMPAT_2_9 \
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 7e5bf86921..db1eecff00 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1276,6 +1276,9 @@ struct X86CPU {
/* KVM automatically enables kvm-pv-eoi if not explicitly disabled by user
*/
bool kvm_auto_enable_pv_eoi;
+ /* KVM automatically enables kvm-pv-unhalt if not explicitly disabled */
+ bool kvm_auto_enable_pv_unhalt;
+
/* Number of physical address bits supported */
uint32_t phys_bits;
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 2160738a37..7461c2a25e 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -3515,6 +3515,11 @@ static void x86_cpu_expand_features(X86CPU *cpu, Error
**errp)
x86_cpu_expand_feature(cpu, FEAT_KVM, (1 << KVM_FEATURE_PV_EOI),
(1 << KVM_FEATURE_PV_EOI));
}
+
+ if (cpu->kvm_auto_enable_pv_unhalt) {
+ x86_cpu_expand_feature(cpu, FEAT_KVM, (1 << KVM_FEATURE_PV_UNHALT),
+ (1 << KVM_FEATURE_PV_UNHALT));
+ }
}
/*TODO: Now cpu->max_features doesn't overwrite features
@@ -4164,6 +4169,8 @@ static Property x86_cpu_properties[] = {
X86CPU, kvm_auto_enable_x2apic, true),
DEFINE_PROP_BOOL("x-kvm-auto-enable-pv-eoi",
X86CPU, kvm_auto_enable_pv_eoi, true),
+ DEFINE_PROP_BOOL("x-kvm-auto-enable-pv-unhalt",
+ X86CPU, kvm_auto_enable_pv_unhalt, true),
DEFINE_PROP_BOOL("vmware-cpuid-freq", X86CPU, vmware_cpuid_freq, true),
DEFINE_PROP_BOOL("tcg-cpuid", X86CPU, expose_tcg, true),
diff --git a/qemu-doc.texi b/qemu-doc.texi
index be45b6b6f6..73c831383a 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -2355,7 +2355,7 @@ Run the emulation in single step mode.
@section KVM kernel module
On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
-require the host to be running Linux v3.6 or newer.
+require the host to be running Linux v3.12 or newer.
@include qemu-tech.texi
--
2.13.6
