insujang / ioat-dma

IOAT-DMA for devdax (device-dax) persistent memory module

This repository contains the following:

• ioat-dma.ko (built from ioat-dma.c): a kernel module that initiates DMA to a DMA device that supports DMA_MEMCPY capability, and handles DMA completion via ioctl(). It depends dax-private.h, which has been borrowed from Linux kernel (linux/drivers/dax).
• test.py (and ioctl_numbers.py): a unittest file built with Python unittest package.
• test.c: a test file that compares performance (DMA vs memcpy).

Build and Test

Tested under Ubuntu 20.04.2 LTS kernel 5.4.0-66-generic. Might not work with higher or lower version of kernel due to inconsistency of dax-private.h. Sources for dax-private.h has been borrowed from Linux kernel 5.6.

/dev/daxX.X is required before executing test files. There is no order dependency between inserting the kernel module and binding DAX devices.

$ make
$ sudo $(ASSISE)/utils/use_dax.sh bind
$ sudo insmod ioat-dma.ko
$ sudo python3 test.py -vv
Randomly generated data: b'(randomly generated)'... (2097152 bytes)
test_01_dax_src_init (__main__.TestIoatDma) ... ok
test_02_ioat_dma (__main__.TestIoatDma) ... ok
test_03_dax_dst_validate (__main__.TestIoatDma) ... ok

----------------------------------------------------------------------
Ran 3 tests in 0.013s

OK
$ sudo ./test
DMA vs memcpy (data size: 0x2000000 bytes)
perform_dma: data verification done!
perform_memcpy: data verification done!
DMA: 0.008604 s, memcpy: 0.015450 s

Using ioat-dma Kernel Module

ioat-dma receives a request from userspace processes via ioctl(), and its ioctl magic number is 0xad.

You can also refer to the function perform_dma() in test.c.

struct ioctl_dma_args {
  char device_name[64];
  uint64_t src_offset;
  uint64_t dst_offset;
  uint64_t size;
} __attribute__ ((packed));
#define IOCTL_IOAT_DMA_SUBMIT _IOW(0xad, 0, struct ioctl_dma_args)

int fd = open("/dev/ioat-dma", O_RDWR);
struct ioctl_dma_args args = {
  .device_name = "/dev/dax0.0",
  .src_offset = src_offset,
  .dst_offset = dst_offset,
  .size = size,
};
ioctl(fd, IOCTL_IOAT_DMA_SUBMIT, &args);
...

This will initiate DMA, copying data from [src_offset, src_offset + size) to [dst_offset, dst_offset + size) with a properly chosen DMA engine.