[0/3,v2] blk-mq: Don't complete in IRQ, use llist_head

Message

Sebastian Andrzej Siewior Dec. 4, 2020, 7:13 p.m. UTC

This a repost of the patches in the old thread [0] which died, rebase against
-next.

The series avoids completing the requests on a remote CPU if booted with
threadirqs. It avoids completing requests in hard-IRQ context on remote
CPU by deferring it to the the softirq context.

One change since the last post: preempt-disable() around llist_add() +
raise_softirq() to ensure that request is added on the same CPU where
the softirq is raised. Some callers (like usb-storage) invoke this
function from preemtible context and this preserves the current "call me
from any context" semantic.
My understanding is that in a later attempt we may change such callers
to complete directly and avoid the softirq ping-pong.

[0] https://lkml.kernel.org/r/[e-mail]

Sebastian