[Devel] [PATCH RHEL7 COMMIT] ms/kvm: disable halt_poll_ns as default for s390x

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-327.10.1.vz7.12.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-327.10.1.vz7.12.11
------>
commit 2dcaa97d42a5d0f2baac8c5cd4fcd28d6b8e8c10
Author: David Hildenbrand <dahi at linux.vnet.ibm.com>
Date:   Tue Apr 19 14:22:51 2016 +0400

    ms/kvm: disable halt_poll_ns as default for s390x
    
    We observed some performance degradation on s390x with dynamic
    halt polling. Until we can provide a proper fix, let's enable
    halt_poll_ns as default only for supported architectures.
    
    Architectures are now free to set their own halt_poll_ns
    default value.
    
    Signed-off-by: David Hildenbrand <dahi at linux.vnet.ibm.com>
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    (cherry picked from commit 920552b213e3dc832a874b4e7ba29ecddbab31bc)
    
    Conflicts:
    	arch/arm64/include/asm/kvm_host.h
    	arch/s390/include/asm/kvm_host.h
    
    Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov at virtuozzo.com>
---
 arch/arm/include/asm/kvm_host.h     | 1 +
 arch/mips/include/asm/kvm_host.h    | 1 +
 arch/powerpc/include/asm/kvm_host.h | 1 +
 arch/s390/include/asm/kvm_host.h    | 2 ++
 arch/x86/include/asm/kvm_host.h     | 1 +
 virt/kvm/kvm_main.c                 | 4 ++--
 6 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
index 1467904..56a4626 100644
--- a/arch/arm/include/asm/kvm_host.h
+++ b/arch/arm/include/asm/kvm_host.h
@@ -32,6 +32,7 @@
 #define KVM_PRIVATE_MEM_SLOTS 4
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 #define KVM_HAVE_ONE_REG
+#define KVM_HALT_POLL_NS_DEFAULT 500000
 
 #define KVM_VCPU_MAX_FEATURES 1
 
diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index adc6b1f..8f70089 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -26,6 +26,7 @@
 #define KVM_PRIVATE_MEM_SLOTS 	0
 
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
+#define KVM_HALT_POLL_NS_DEFAULT 500000
 
 /* Don't support huge pages */
 #define KVM_HPAGE_GFN_SHIFT(x)	0
diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index 69c2389..b6f246b 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -44,6 +44,7 @@
 #ifdef CONFIG_KVM_MMIO
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
 #endif
+#define KVM_HALT_POLL_NS_DEFAULT 500000
 
 /* These values are internal and can be increased later */
 #define KVM_NR_IRQCHIPS          1
diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index 297b2c3..ec35578 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -25,6 +25,8 @@
 #define KVM_MAX_VCPUS 64
 #define KVM_USER_MEM_SLOTS 32
 
+#define KVM_HALT_POLL_NS_DEFAULT 0
+
 struct sca_entry {
 	atomic_t scn;
 	__u32	reserved;
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a73a3bb..f81eafd 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -43,6 +43,7 @@
 
 #define KVM_PIO_PAGE_OFFSET 1
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 2
+#define KVM_HALT_POLL_NS_DEFAULT 500000
 
 #define KVM_IRQCHIP_NUM_PINS  KVM_IOAPIC_NUM_PINS
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 1fc1f12..870c968 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -66,8 +66,8 @@
 MODULE_AUTHOR("Qumranet");
 MODULE_LICENSE("GPL");
 
-/* halt polling only reduces halt latency by 5-7 us, 500us is enough */
-static unsigned int halt_poll_ns = 500000;
+/* Architectures should define their poll value according to the halt latency */
+static unsigned int halt_poll_ns = KVM_HALT_POLL_NS_DEFAULT;
 module_param(halt_poll_ns, uint, S_IRUGO | S_IWUSR);
 
 /* Default doubles per-vcpu halt_poll_ns. */