Il 20/08/2014 09:16, Paolo Bonzini ha scritto:
> Il 19/08/2014 22:35, Radim Krčmář ha scritto:
>> Every increase of ple_window_grow creates potential overflows.
>> They are not serious, because we clamp ple_window and userspace is
>> expected to fix ple_window_max within a second.
>> ---
>> arch/x86/kvm/vmx.c | 34 +++++++++++++++++++++++++++++++++-
>> 1 file changed, 33 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index d7f58e8..6873a0b 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -138,7 +138,9 @@ module_param(ple_window, int, S_IRUGO | S_IWUSR);
>>
>> /* Default doubles per-vcpu window every exit. */
>> static int ple_window_grow = KVM_VMX_DEFAULT_PLE_WINDOW_GROW;
>> -module_param(ple_window_grow, int, S_IRUGO | S_IWUSR);
>> +static struct kernel_param_ops ple_window_grow_ops;
>> +module_param_cb(ple_window_grow, &ple_window_grow_ops,
>> + &ple_window_grow, S_IRUGO | S_IWUSR);
>>
>> /* Default resets per-vcpu window every exit to ple_window. */
>> static int ple_window_shrink = KVM_VMX_DEFAULT_PLE_WINDOW_SHRINK;
>> @@ -5717,6 +5719,36 @@ static void type##_ple_window(struct kvm_vcpu *vcpu) \
>> make_ple_window_modifier(grow, *, +) /* grow_ple_window */
>> make_ple_window_modifier(shrink, /, -) /* shrink_ple_window */
>>
>> +static void clamp_ple_window_max(void)
>> +{
>> + int maximum;
>> +
>> + if (ple_window_grow < 1)
>> + return;
>> +
>> + if (ple_window_grow < ple_window)
>> + maximum = INT_MAX / ple_window_grow;
>> + else
>> + maximum = INT_MAX - ple_window_grow;
>> +
>> + ple_window_max = clamp(ple_window_max, ple_window, maximum);
>> +}
>
> I think avoiding overflows is better. In fact, I think you should call
> this function for ple_window_max too.
>
> You could keep the ple_window_max variable to the user-set value.
> Whenever ple_window_grow or ple_window_max are changed, you can set an
> internal variable (let's call it ple_window_actual_max, but I'm not wed
> to this name) to the computed value, and then do:
>
> if (ple_window_grow < 1 || ple_window_actual_max < ple_window)
> new = ple_window;
> else if (ple_window_grow < ple_window)
> new = max(ple_window_actual_max, old) * ple_window_grow;
> else
> new = max(ple_window_actual_max, old) + ple_window_grow;
Ehm, this should of course be "min".
Paolo
> (I think the || in the first "if" can be eliminated with some creativity
> in clamp_ple_window_max).
>
> Paolo
>
>> +static int set_ple_window_grow(const char *arg, const struct kernel_param
>> *kp)
>> +{
>> + int ret;
>> +
>> + clamp_ple_window_max();
>> + ret = param_set_int(arg, kp);
>> +
>> + return ret;
>> +}
>> +
>> +static struct kernel_param_ops ple_window_grow_ops = {
>> + .set = set_ple_window_grow,
>> + .get = param_get_int,
>> +};
>> +
>> /*
>> * Indicate a busy-waiting vcpu in spinlock. We do not enable the PAUSE
>> * exiting, so only get here on cpu with PAUSE-Loop-Exiting.
>>
>
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