[PATCHSET v4 next 0/5] Add support for non-IPI task_work

Jens Axboe
2022-04-26T01:49:15Z

Hi,

Unless we're using SQPOLL, any task_work queue will result in an IPI
to the target task unless it's running in the kernel already. This isn't
always needed, particularly not for the common case of not sharing the
ring. In certain workloads, this can provide a 5-10% improvement. Some
of this is due the cost of the IPI, and some from needlessly
interrupting the target task when the work could just get run when
completions are being waited for.

Patches 1..4 are prep patches, patch 5 is the actual change, and patch 6
adds support for IORING_SQ_TASKRUN so that applications may use this
feature and still rely on io_uring_peek_cqe().

v4:
- Make SQPOLL incompatible with the IPI flags. It makes no sense for
SQPOLL as no IPIs are ever used there anyway, so make that explicit
and fail a request to setup a ring like that.