Re: [PATCH v3 2/4] vfio: selftests: Introduce vfio_dma_mapping_perf_test

[David Matlack <dmatlack@google.com>]

On 2026-09-10 03:33 PM, Aaron Lewis wrote:
> Introduce vfio_dma_mapping_perf_test to aid in latency testing. Rather
> than a traditional pass/fail test, which tends to be flaky when
> enforcing latency bounds, this test directly reports the latency of
> various stages in the mapping and unmapping process.
> 
> Start with a basic test that performs a simple DMA map/unmap and tracks
> the duration of each operation. The test reports the following metrics:
> 
> 1. Time taken by mmap().
> 2. Time taken to map a DMA region.
> 3. Time taken to unmap a DMA region.
> 4. Time taken by munmap().
> 
> Subsequent commits in this series will introduce more features to allow
> for a wider variety of testing.
> 
> To ensure consistent DMA mapping times, the test uses MAP_POPULATE when
> calling mmap(). This forces page faults to be handled upfront, isolating
> the DMA mapping times from them.
> 
> Signed-off-by: Aaron Lewis <aaronlewis@google.com>

Aside from the nit,

Reviewed-by: David Matlack <dmatlack@google.com>

> ---
>  tools/testing/selftests/vfio/Makefile         |  1 +
>  .../selftests/vfio/lib/include/libvfio.h      | 31 +++++++
>  .../vfio/vfio_dma_mapping_perf_test.c         | 90 +++++++++++++++++++
>  3 files changed, 122 insertions(+)
>  create mode 100644 tools/testing/selftests/vfio/vfio_dma_mapping_perf_test.c
> 
> diff --git a/tools/testing/selftests/vfio/Makefile b/tools/testing/selftests/vfio/Makefile
> index 2c32c48db509..ed5856af5f9a 100644
> --- a/tools/testing/selftests/vfio/Makefile
> +++ b/tools/testing/selftests/vfio/Makefile
> @@ -8,6 +8,7 @@ else
>  CFLAGS = $(KHDR_INCLUDES)
>  TEST_GEN_PROGS += vfio_dma_mapping_test
>  TEST_GEN_PROGS += vfio_dma_mapping_mmio_test
> +TEST_GEN_PROGS += vfio_dma_mapping_perf_test
>  TEST_GEN_PROGS += vfio_iommufd_setup_test
>  TEST_GEN_PROGS += vfio_pci_device_test
>  TEST_GEN_PROGS += vfio_pci_device_init_perf_test
> diff --git a/tools/testing/selftests/vfio/lib/include/libvfio.h b/tools/testing/selftests/vfio/lib/include/libvfio.h
> index 07862b470777..8496b8b4da3c 100644
> --- a/tools/testing/selftests/vfio/lib/include/libvfio.h
> +++ b/tools/testing/selftests/vfio/lib/include/libvfio.h
> @@ -9,6 +9,37 @@
>  #include <libvfio/vfio_pci_device.h>
>  #include <libvfio/vfio_pci_driver.h>
>  
> +#include <stdint.h>
> +#include <time.h>
> +#include <linux/time64.h>
> +
> +static inline void timer_start(struct timespec *start)
> +{
> +	clock_gettime(CLOCK_MONOTONIC, start);
> +}
> +
> +static inline uint64_t timer_elapsed_ns(struct timespec start)
> +{
> +	struct timespec end;
> +
> +	clock_gettime(CLOCK_MONOTONIC, &end);

Maybe rename timer_start() to timer_get() and re-use it here.