Patch "KVM: x86: reduce default value of halt_poll_ns parameter" has been added to the 4.4-stable tree

Patch "KVM: x86: reduce default value of halt_poll_ns parameter" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    KVM: x86: reduce default value of halt_poll_ns parameter

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-x86-reduce-default-value-of-halt_poll_ns-parameter.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 14ebda3394fd3e5388747e742e510b0802a65d24 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Tue, 29 Mar 2016 17:56:57 +0200
Subject: KVM: x86: reduce default value of halt_poll_ns parameter

From: Paolo Bonzini <pbonzini@redhat.com>

commit 14ebda3394fd3e5388747e742e510b0802a65d24 upstream.

Windows lets applications choose the frequency of the timer tick,
and in Windows 10 the maximum rate was changed from 1024 Hz to
2048 Hz.  Unfortunately, because of the way the Windows API
works, most applications who need a higher rate than the default
64 Hz will just do

   timeGetDevCaps(&tc, sizeof(tc));
   timeBeginPeriod(tc.wPeriodMin);

and pick the maximum rate.  This causes very high CPU usage when
playing media or games on Windows 10, even if the guest does not
actually use the CPU very much, because the frequent timer tick
causes halt_poll_ns to kick in.

There is no really good solution, especially because Microsoft
could sooner or later bump the limit to 4096 Hz, but for now
the best we can do is lower a bit the upper limit for
halt_poll_ns. :-(

Reported-by: Jon Panozzo <jonp@lime-technology.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/include/asm/kvm_host.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -41,7 +41,7 @@
 
 #define KVM_PIO_PAGE_OFFSET 1
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 2
-#define KVM_HALT_POLL_NS_DEFAULT 500000
+#define KVM_HALT_POLL_NS_DEFAULT 400000
 
 #define KVM_IRQCHIP_NUM_PINS  KVM_IOAPIC_NUM_PINS
 


Patches currently in stable-queue which might be from pbonzini@redhat.com are

queue-4.4/kvm-x86-inject-pending-interrupt-even-if-pending-nmi-exist.patch
queue-4.4/kvm-x86-reduce-default-value-of-halt_poll_ns-parameter.patch
queue-4.4/compiler-gcc-disable-ftracer-for-__noclone-functions.patch