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

[Josh Hilke <jrhilke@google.com>]

On Wed, Apr 01, 2026 at 01:01:42PM -0700, Sean Christopherson wrote:
> 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.
> 

Ah, my bad didn't know there was a checkpatch script. Will do.

> > @@ -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.
> 

Will do in v3. 

> >  	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.
> 

I'll create a helper and add it to that library in v3.

> > +
> >  	/* 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
> >