dma-mapping: provide a benchmark for streaming DMA mapping · Pull Request !233 · openEuler/kernel

Nowadays, there are increasing requirements to benchmark the performance
of dma_map and dma_unmap particually while the device is attached to an
IOMMU.

This patchset provides the benchmark infrastruture for streaming DMA
mapping. The architecture of the code is pretty much similar with GUP
benchmark:

mm/gup_benchmark.c provides kernel interface;
tools/testing/selftests/vm/gup_benchmark.c provides user program to
call the interface provided by mm/gup_benchmark.c.
In our case, kernel/dma/map_benchmark.c is like mm/gup_benchmark.c;
tools/testing/selftests/dma/dma_map_benchmark.c is like tools/testing/
selftests/vm/gup_benchmark.c

A major difference with GUP benchmark is DMA_MAP benchmark needs to run
on a device. Considering one board with below devices and IOMMUs
device A ------- IOMMU 1
device B ------- IOMMU 2
device C ------- non-IOMMU

Different devices might attach to different IOMMU or non-IOMMU. To make
benchmark run, we can either

create a virtual device and hack the kernel code to attach the virtual
device to IOMMU1, IOMMU2 or non-IOMMU.
use the existing driver_override mechinism, unbind device A,B, OR c from
their original driver and bind A to dma_map_benchmark platform driver or
pci driver for benchmarking.
In this patchset, I prefer to use the driver_override and avoid the ugly
hack in kernel. We can dynamically switch device behind different IOMMUs
to get the performance of IOMMU or non-IOMMU.

This patch provides the test application for DMA_MAP_BENCHMARK.

Before running the test application, we need to bind a device to dma_map_benchmark driver. For example, unbind "xxx" from its original driver and bind to dma_map_benchmark:

echo dma_map_benchmark > /sys/bus/platform/devices/xxx/driver_override
echo xxx > /sys/bus/platform/drivers/xxx/unbind
echo xxx > /sys/bus/platform/drivers/dma_map_benchmark/bind

Another example for PCI devices:
echo dma_map_benchmark > /sys/bus/pci/devices/0000:00:01.0/driver_override
echo 0000:00:01.0 > /sys/bus/pci/drivers/xxx/unbind
echo 0000:00:01.0 > /sys/bus/pci/drivers/dma_map_benchmark/bind

The below command will run 16 threads on numa node 0 for 10 seconds on the device bound to dma_map_benchmark platform_driver or pci_driver:
./dma_map_benchmark -t 16 -s 10 -n 0
dma mapping benchmark: threads:16 seconds:10
average map latency(us):1.1 standard deviation:1.9
average unmap latency(us):0.5 standard deviation:0.8

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