# (unknown)

- From: Vikas Aggarwal \<hidden\>
- Date: 2016-06-05 12:28:22 
- List: linux-raid
- Page: https://ratatoskr.run/linux-raid/2016/06/6632210
- Thread: https://ratatoskr.run/linux-raid/2016/06/6632210/t.md

```text
Hello All,

Will appreciate if someone can clear my doubts regarding  XOR/GF
offload for raid5/6.

1) What is the purpose of device_prep_dma_interrupt  callback ?

2) My driver currently polls for checking the xor  completions
 and does'nt implement device_prep_dma_interrupt
callback at all.  What  performance variation  I can expect  by
implementing this callback
in my async_tx driver.

3) Purpose of DMA_ACK as I read - it is  for higher layers to inform
dma driver that descriptors can now be freed. Can someone explain this
with an example as applicable with raid5/6 clients.

4) With example - why dma_run_dependencies(tx) needed  after the
hardware engine posts completion for a descriptor.

5) Purpose of  tx->callback(cb_arg) - again with an example from a
raid5/6 offload perspective.

Goal: I want to use offload engine efficiently with recent
multithreaded raid5/6.

I tried to dig through code and linux/Documentation etc but not
thoroughly clear of functionality.

Thanks & Regards
Vikas Aggarwal
```