Re: [RFC 00/11] io_uring specific task_work infra

[Pavel Begunkov <asml.silence@gmail.com>]

On 4/21/22 14:44, Pavel Begunkov wrote:
> For experiments only. If proves to be useful would need to make it
> nicer on the non-io_uring side.
> 
> 0-10 save 1 spinlock/unlock_irq pair and 2 cmpxchg per batch. 11/11 in
> general trades 1 per tw add spin_lock/unlock_irq and 2 per batch spinlocking
> with 2 cmpxchg to 1 per tw add cmpxchg and 1 per batch cmpxchg.

null_blk irqmode=1 completion_nsec=0 submit_queues=32 poll_queues=32
echo -n 0 > /sys/block/nullb0/queue/iostats
echo -n 2 > /sys/block/nullb0/queue/nomerges
io_uring -d<QD> -s<QD> -c<QD> -p0 -B1 -F1 -b512 /dev/nullb0


      | base | 1-10         | 1-11
___________________________________________
QD1  | 1.88 | 2.15 (+14%)  | 2.19 (+16.4%)
QD4  | 2.8  | 3.06 (+9.2%) | 3.11 (+11%)
QD32 | 3.61 | 3.81 (+5.5%) | 3.96 (+9.6%)

The numbers are in MIOPS, (%) is relative diff with the baseline.
It gives more than I expected, but the testing is not super
consistent, so a part of it might be due to variance.


> Pavel Begunkov (11):
>    io_uring: optimise io_req_task_work_add
>    io_uringg: add io_should_fail_tw() helper
>    io_uring: ban tw queue for exiting processes
>    io_uring: don't take ctx refs in tctx_task_work()
>    io_uring: add dummy io_uring_task_work_run()
>    task_work: add helper for signalling a task
>    io_uring: run io_uring task_works on TIF_NOTIFY_SIGNAL
>    io_uring: wire io_uring specific task work
>    io_uring: refactor io_run_task_work()
>    io_uring: remove priority tw list
>    io_uring: lock-free task_work stack
> 
>   fs/io-wq.c                |   1 +
>   fs/io_uring.c             | 213 +++++++++++++++-----------------------
>   include/linux/io_uring.h  |   4 +
>   include/linux/task_work.h |   4 +
>   kernel/entry/kvm.c        |   1 +
>   kernel/signal.c           |   2 +
>   kernel/task_work.c        |  33 +++---
>   7 files changed, 115 insertions(+), 143 deletions(-)
> 

-- 
Pavel Begunkov