Currently selecting KVM guest support enabled multiple features at once that
not everyone necessarily wants to have, namely:
- PV MMU
- zero io delay
- apic detection workaround
Let's split them off so we don't drag in the full pv-ops framework just to
detect we're running on KVM. That gives us more chances to tweak performance!
Signed-off-by: Alexander Graf <ag...@suse.de>
---
arch/x86/Kconfig | 29 ++++++++++++++++++++++++++++-
arch/x86/kernel/kvm.c | 22 +++++++++++++++-------
2 files changed, 43 insertions(+), 8 deletions(-)
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8c150b6..97d4f92 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -522,11 +522,38 @@ config KVM_CLOCK
config KVM_GUEST
bool "KVM Guest support"
- select PARAVIRT_ALL
+ select PARAVIRT
---help---
This option enables various optimizations for running under the KVM
hypervisor.
+config KVM_IODELAY
+ bool "KVM IO-delay support"
+ depends on KVM_GUEST
+ select PARAVIRT_CPU
+ ---help---
+ Usually we wait for PIO access to complete. When inside KVM there's
+ no need to do that, as we know that we're not going through a bus,
+ but process PIO requests instantly.
+
+ This option disables PIO waits, but drags in CPU-bound pv-ops. Thus
+ you will probably get more speed loss than speedup using this option.
+
+ If in doubt, say N.
+
+config KVM_MMU
+ bool "KVM PV MMU support"
+ depends on KVM_GUEST
+ select PARAVIRT_MMU
+ ---help---
+ This option enables the paravirtualized MMU for KVM. In most cases
+ it's pretty useless and shouldn't be used.
+
+ It will only cost you performance, because it drags in pv-ops for
+ memory management.
+
+ If in doubt, say N.
+
source "arch/x86/lguest/Kconfig"
config PARAVIRT
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 63b0ec8..7e0207f 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -29,6 +29,16 @@
#include <linux/hardirq.h>
#include <asm/timer.h>
+#ifdef CONFIG_KVM_IODELAY
+/*
+ * No need for any "IO delay" on KVM
+ */
+static void kvm_io_delay(void)
+{
+}
+#endif /* CONFIG_KVM_IODELAY */
+
+#ifdef CONFIG_KVM_MMU
#define MMU_QUEUE_SIZE 1024
struct kvm_para_state {
@@ -43,13 +53,6 @@ static struct kvm_para_state *kvm_para_state(void)
return &per_cpu(para_state, raw_smp_processor_id());
}
-/*
- * No need for any "IO delay" on KVM
- */
-static void kvm_io_delay(void)
-{
-}
-
static void kvm_mmu_op(void *buffer, unsigned len)
{
int r;
@@ -194,15 +197,19 @@ static void kvm_leave_lazy_mmu(void)
mmu_queue_flush(state);
paravirt_leave_lazy_mmu();
}
+#endif /* CONFIG_KVM_MMU */
static void __init paravirt_ops_setup(void)
{
pv_info.name = "KVM";
pv_info.paravirt_enabled = 1;
+#ifdef CONFIG_KVM_IODELAY
if (kvm_para_has_feature(KVM_FEATURE_NOP_IO_DELAY))
pv_cpu_ops.io_delay = kvm_io_delay;
+#endif
+#ifdef CONFIG_KVM_MMU
if (kvm_para_has_feature(KVM_FEATURE_MMU_OP)) {
pv_mmu_ops.set_pte = kvm_set_pte;
pv_mmu_ops.set_pte_at = kvm_set_pte_at;
@@ -226,6 +233,7 @@ static void __init paravirt_ops_setup(void)
pv_mmu_ops.lazy_mode.enter = kvm_enter_lazy_mmu;
pv_mmu_ops.lazy_mode.leave = kvm_leave_lazy_mmu;
}
+#endif /* CONFIG_KVM_MMU */
#ifdef CONFIG_X86_IO_APIC
no_timer_check = 1;
#endif
--
1.6.0.2
--
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