driver

SLASH kernel module

Module parameters

Exposed under /sys/module/slash/parameters/ (all writable at runtime; see modinfo slash.ko):

Parameter	Type	Default	Description
qdma_num_threads	uint	8	Number of libqdma worker threads.
qdma_debugfs_path	charp	disabled	debugfs mount path for libqdma.

A/B testing NoC channel bandwidth

The AXI-MM / NoC channel is chosen per queue pair when it is added (the mm_channel field of the qpair-add ioctl, enum slash_qdma_mm_channel): auto stripes queues across both channels by qid & 1, while 0 / 1 pin a queue to a single channel. Every queue creator carries this setting, so it can be driven per buffer to check whether both PCIe NMUs (NoC channels) actually contribute bandwidth. With v80-smi validate:

# All queues on NoC channel 0 (NMU S00)
sudo v80-smi validate -d <BDF> --raw-transfer-test --no-reset --mm-channel 0

# All queues on NoC channel 1 (NMU S01)
sudo v80-smi validate -d <BDF> --raw-transfer-test --no-reset --mm-channel 1

# Split across both channels (qid & 1)
sudo v80-smi validate -d <BDF> --raw-transfer-test --no-reset --mm-channel auto

# Explicit per-buffer split (even positions -> channel 0, odd -> channel 1)
sudo v80-smi validate -d <BDF> --raw-transfer-test --no-reset --mm-channel 0,1

Debug builds with SLASH_QDMA_OP_DEBUG=1 log each queue's selected mm_channel when it is added. If the split run is no faster than a single forced channel, traffic is not being spread across both NMUs. The per-queue setting affects every queue created through this driver (both the VRTD buffer path and --raw-transfer-test); the off-the-shelf Xilinx QDMA driver path (--use-qdma-driver) honors --mm-channel through its own channel attribute.

Testing

The test suite requires a physical V80 to be present and the module to be loaded into a running kernel.

Local libqdma patches

SLASH carries small patches for the pinned libqdma submodule under driver/patches/. The driver Makefile applies them before building, and make clean attempts to revert them so the submodule working copy returns to its pristine pinned state. DKMS packages include the same patch directory and depend on patch(1).

Prerequisites

• A kernel built with CONFIG_GCOV_KERNEL=y (only needed for coverage runs).
• lcov and genhtml installed (only needed for coverage runs).
• The BDF identifier of the V80 card (e.g. 0000:03:00).
  • You may be able to retrieve the BDF identifier by running v80-smi list

Running the tests manually

Build the module and the test suite:

make          # builds slash.ko
make -C tests/ all

Load the module and rescan the PCI bus so the device nodes appear:

sudo insmod ./slash.ko
echo 1 | sudo tee /sys/bus/pci/rescan > /dev/null

Run the kselftest suite (must be run as root):

sudo make -C tests/ run

The suite produces TAP output. Each test fixture automatically tears down queue pairs on failure, so a failing test does not leave the device in a broken state.

Optional: override the DMA target address

The write_read_verify test defaults to DMA address 0x0. Set SLASH_TEST_DMA_ADDR to use a different address:

sudo SLASH_TEST_DMA_ADDR=0x100000000 make -C tests/ run

Running with code-coverage instrumentation

test_module.sh automates the full build → load → test → coverage cycle:

./test_module.sh <BBBB:DD:FF>

Replace <BBBB:DD:FF> with the BDF of the V80 (e.g. 0000:03:00).

The script:

1. Checks that the running kernel has CONFIG_GCOV_KERNEL=y.
2. Builds slash.ko with gcov instrumentation (make GCOV=1).
3. Builds the test suite.
4. Removes any currently-loaded slash module.
5. Resets the gcov counters.
6. Inserts the module and rescans the PCI bus.
7. Runs the full kselftest suite.
8. Removes the module.
9. Captures coverage with lcov and generates an HTML report in coverage/.

Open coverage/index.html in a browser to browse line-level coverage.