Comment 29 for bug 1838575

(systemtap)
probe module("vfio_iommu_type1").function("vfio_iommu_type1_ioctl") {
    printf("New vfio_iommu_type1_ioctl\n");
    start_stopwatch("vfioioctl");
}
probe module("vfio_iommu_type1").function("vfio_iommu_type1_ioctl").return {
    timer=read_stopwatch_ns("vfioioctl")
    printf("Completed vfio_iommu_type1_ioctl: %d\n", timer);
    stop_stopwatch("vfioioctl");
}
probe module("vfio_iommu_type1").function("vfio_pin_pages_remote") {
    timer=read_stopwatch_ns("vfioioctl")
    printf("%ld: %s\n", timer, $$parms);
}

The overhead was significant enough, the fast case this time was 132 seconds.
The following slow case had 209 seconds (still slower but not more by factors).

While the overhead might have influenced the absolute timing of this too much.
It still might help indicate the size/frequency distribution of these calls that we wanted to know.