Re: [PATCH RFC 0/9] nxt propagation + locking optimisation

[Pavel Begunkov]

On 01/03/2020 19:18, Pavel Begunkov wrote:
> There are several independent parts in the patchset, but bundled
> to make a point.
> 1-2: random stuff, that implicitly used later.
> 3-5: restore @nxt propagation
> 6-8: optimise locking in io_worker_handle_work()
> 9: optimise io_uring refcounting
> 
> The next propagation bits are done similarly as it was before, but
> - nxt stealing is now at top-level, but not hidden in handlers
> - ensure there is no with REQ_F_DONT_STEAL_NEXT
> 
> [6-8] is the reason to dismiss the previous @nxt propagation appoach,
> I didn't found a good way to do the same. Even though it looked
> clearer and without new flag.
> 
> Performance tested it with link-of-nops + IOSQE_ASYNC:
> 
> link size: 100
> orig:  501 (ns per nop)
> 0-8:   446
> 0-9:   416
> 
> link size: 10
> orig:  826
> 0-8:   776
> 0-9:   756

BTW, that's basically QD1, and with contention for wqe->lock the gap should be
even wider.

> 
> Pavel Begunkov (9):
>   io_uring: clean up io_close
>   io-wq: fix IO_WQ_WORK_NO_CANCEL cancellation
>   io_uring: make submission ref putting consistent
>   io_uring: remove @nxt from handlers
>   io_uring: get next req on subm ref drop
>   io-wq: shuffle io_worker_handle_work() code
>   io-wq: io_worker_handle_work() optimise locking
>   io-wq: optimise double lock for io_get_next_work()
>   io_uring: pass submission ref to async
> 
>  fs/io-wq.c    | 162 ++++++++++++----------
>  fs/io_uring.c | 366 ++++++++++++++++++++++----------------------------
>  2 files changed, 258 insertions(+), 270 deletions(-)
> 

-- 
Pavel Begunkov