Hi Marc, Christoffer,
On 2014/11/23 4:04, Christoffer Dall wrote:
> On Wed, Nov 19, 2014 at 06:11:25PM +0800, Shannon Zhao wrote:
>> When call kvm_vgic_inject_irq to inject interrupt, we can known which
>> vcpu the interrupt for by the irq_num and the cpuid. So we should just
>> kick this vcpu to avoid iterating through all.
>>
>> Signed-off-by: Shannon Zhao <zhaoshenglong@xxxxxxxxxx>
>
> This looks reasonable to me:
>
> Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
>
> But as Marc said, we have to consider the churn by introducing more
> changes to the vgic (that file is being hammered pretty intensely
> these days), so if you feel this is an urgent optimization, it would
> be useful to see some data backing this up.
>
Today I have a test which measures the cycles about kvm_vgic_inject_irq by PMU.
I just test the cycles of SPI using virtio-net.
Test steps:
1) start a VM with 8 VCPUs
2) In guest bind the irq of virtio to CPU8, host ping VM, get the cycles
The test shows:
Without this patch, the cycles is about 3700(3300-5000), and with this patch, the cycles is about 3000(2500-3200).
>From this test, I think this patch can bring some improvements.
The test code like below. As it's almost no difference about vgic_update_irq_state
between with and without this patch. So just measure the kick's cycles.
int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
bool level)
{
unsigned long cycles_1,cycles_2;
if (likely(vgic_initialized(kvm)) &&
vgic_update_irq_pending(kvm, cpuid, irq_num, level)) {
start_pmu();
__asm__ __volatile__("MRS %0, PMCCNTR_EL0" : "=r"(cycles_1));
vgic_kick_vcpus(kvm);
__asm__ __volatile__("MRS %0, PMCCNTR_EL0" : "=r"(cycles_2));
}
return 0;
}
int kvm_vgic_inject_irq(struct kvm *kvm, int cpuid, unsigned int irq_num,
bool level)
{
int vcpu_id;
unsigned long cycles_a,cycles_b;
if (likely(vgic_initialized(kvm))) {
vcpu_id = vgic_update_irq_pending(kvm, cpuid, irq_num, level);
if (vcpu_id >= 0) {
start_pmu();
__asm__ __volatile__("MRS %0, PMCCNTR_EL0" : "=r"(cycles_a));
/* kick the specified vcpu */
kvm_vcpu_kick(kvm_get_vcpu(kvm, vcpu_id));
__asm__ __volatile__("MRS %0, PMCCNTR_EL0" : "=r"(cycles_b));
}
}
return 0;
}
Thanks,
Shannon
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