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KVM: VMX: increase ple_gap default to 128

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On some CPUs, a ple_gap of 41 is simply insufficient to ever trigger
PLE exits, even with the minimalistic PLE test from kvm-unit-tests.

http://git.kernel.org/?p=virt/kvm/kvm-unit-tests.git;a=commitdiff;h=eda71b28fa122203e316483b35f37aaacd42f545

For example, the Xeon X5670 CPU needs a ple_gap of at least 48 in
order to get pause loop exits:

# modprobe kvm_intel ple_gap=47
# taskset 1 /usr/local/bin/qemu-system-x86_64 \
  -device testdev,chardev=log -chardev stdio,id=log \
  -kernel x86/vmexit.flat -append ple-round-robin -smp 2
VNC server running on `::1:5900'
enabling apic
enabling apic
ple-round-robin 58298446
# rmmod kvm_intel
# modprobe kvm_intel ple_gap=48
# taskset 1 /usr/local/bin/qemu-system-x86_64 \
   -device testdev,chardev=log -chardev stdio,id=log \
   -kernel x86/vmexit.flat -append ple-round-robin -smp 2
VNC server running on `::1:5900'
enabling apic
enabling apic
ple-round-robin 36616

Increase the ple_gap to 128 to be on the safe side.

Signed-off-by: Rik van Riel <riel@redhat.com>
Acked-by: Zhai, Edwin <edwin.zhai@intel.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Rik van Riel 2011-01-04 09:51:33 -05:00 committed by Marcelo Tosatti
parent 3781c01c15
commit 00c25bce02
1 changed files with 2 additions and 2 deletions
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4
arch/x86/kvm/vmx.c
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@ -93,14 +93,14 @@ module_param(yield_on_hlt, bool, S_IRUGO);
* These 2 parameters are used to config the controls for Pause-Loop Exiting:
* ple_gap: upper bound on the amount of time between two successive
* executions of PAUSE in a loop. Also indicate if ple enabled.
* According to test, this time is usually small than 41 cycles.
* According to test, this time is usually smaller than 128 cycles.
* ple_window: upper bound on the amount of time a guest is allowed to execute
* in a PAUSE loop. Tests indicate that most spinlocks are held for
* less than 2^12 cycles
* Time is measured based on a counter that runs at the same rate as the TSC,
* refer SDM volume 3b section 21.6.13 & 22.1.3.
*/
#define KVM_VMX_DEFAULT_PLE_GAP 41
#define KVM_VMX_DEFAULT_PLE_GAP 128
#define KVM_VMX_DEFAULT_PLE_WINDOW 4096
static int ple_gap = KVM_VMX_DEFAULT_PLE_GAP;
module_param(ple_gap, int, S_IRUGO);