Re: [PATCH v2 05/14] KVM: selftests: Add support for random host IRQ affinity

[Sean Christopherson <seanjc@google.com>]

On Tue, Mar 31, 2026, Josh Hilke wrote:
> From: David Matlack <dmatlack@google.com>
> 
> Add the '-a' flag to vfio_pci_irq_test to randomly affinitize the
> device's host IRQ to different physical CPUs throughout the test.  This
> stresses the kernel's ability to maintain correct interrupt routing and
> delivery even as the underlying hardware IRQ affinity is changed
> dynamically via /proc/irq/.
> 
> Signed-off-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Josh Hilke <jrhilke@google.com>
> Co-developed-by: Josh Hilke <jrhilke@google.com>

Please run checkpatch, the order here is wrong.

> @@ -122,13 +125,19 @@ int main(int argc, char **argv)
>  	struct vfio_pci_device *device;
>  	struct iommu *iommu;
>  	const char *device_bdf;
> +	FILE *irq_affinity_fp;
>  	int i, j, c, msi, irq;
>  	struct kvm_vm *vm;
> +	int irq_cpu;
> +	int ret;

Use the existing "int" declaration.

>  	device_bdf = vfio_selftests_get_bdf(&argc, argv);
>  
> -	while ((c = getopt(argc, argv, "h")) != -1) {
> +	while ((c = getopt(argc, argv, "ah")) != -1) {
>  		switch (c) {
> +		case 'a':
> +			irq_affinity = true;
> +			break;
>  		case 'h':
>  		default:
>  			help(argv[0]);
> @@ -163,6 +172,14 @@ int main(int argc, char **argv)
>  			continue;
>  	}
>  
> +	if (irq_affinity) {
> +		char path[PATH_MAX];
> +
> +		snprintf(path, sizeof(path), "/proc/irq/%d/smp_affinity_list", irq);
> +		irq_affinity_fp = fopen(path, "w");
> +		TEST_ASSERT(irq_affinity_fp, "fopen(%s) failed", path);
> +	}

This plus setting the affinity is begging for a library function, probably
provided by what's currently called get_irq_number() and friends.

> +
>  	/* Set a consistent seed so that test are repeatable. */
>  	srand(0);
>  
> @@ -172,6 +189,13 @@ int main(int argc, char **argv)
>  
>  		kvm_route_msi(vm, gsi, vcpu, vector);
>  
> +		if (irq_affinity && vcpu->id == 0) {
> +			irq_cpu = rand() % get_nprocs();
> +
> +			ret = fprintf(irq_affinity_fp, "%d\n", irq_cpu);
> +			TEST_ASSERT(ret > 0, "Failed to affinitize IRQ-%d to CPU %d", irq, irq_cpu);
> +		}
> +
>  		for (j = 0; j < nr_vcpus; j++) {
>  			TEST_ASSERT(
>  				!READ_FROM_GUEST(vm, guest_received_irq[vcpu->id]),
> @@ -189,6 +213,8 @@ int main(int argc, char **argv)
>  			if (timespec_to_ns(timespec_elapsed(start)) > TIMEOUT_NS) {
>  				printf("Timeout waiting for interrupt!\n");
>  				printf("  vCPU: %d\n", vcpu->id);
> +				if (irq_affinity)
> +					printf("  irq_cpu: %d\n", irq_cpu);
>  
>  				TEST_FAIL("vCPU never received IRQ!\n");
>  			}
> @@ -203,6 +229,9 @@ int main(int argc, char **argv)
>  		pthread_join(vcpu_threads[i], NULL);
>  	}
>  
> +	if (irq_affinity)
> +		fclose(irq_affinity_fp);
> +
>  	printf("Host interrupts handled:\n");
>  	printf("  IRQ-%d: %lu\n", irq, get_irq_count(irq) - irq_count);
>  	printf("  Posted-interrupt notification events: %lu\n",
> -- 
> 2.53.0.1118.gaef5881109-goog
>