[PATCHSET,RFC,0/4] Add support for epoll min_wait

Message

Jens Axboe Oct. 7, 2022, 4:56 p.m. UTC

Hi,

This adds support for EPOLL_CTL_MIN_WAIT, which allows setting a minimum
time that epoll_wait() should wait for events on a given epoll context.
Some justification and numbers are in patch 4, patches 1-3 are really
just prep patches.

Sending this as an RFC to hash out the API, basically. This is
obviously a per-context type of operation in this patchset, which isn't
necessarily ideal for any use case. Questions to be debated:

1) Would we want this to be available through epoll_wait() directly?
   That would allow this to be done on a per-epoll_wait() basis, rather
   than be tied to the specific context.

2) If the answer to #1 is yes, would we still want EPOLL_CTL_MIN_WAIT?

I think there are pros and cons to both, and perhaps the answer to both
is "yes". There are some benefits to doing this at epoll setup time,
for example - it nicely isolates it to that part rather than needing
to be done dynamically everytime epoll_wait() is called. This also
helps the application code, as it can turn off any busy'ness tracking
based on if the setup accepted EPOLL_CTL_MIN_WAIT or not.

Anyway, tossing this out there as it yielded quite good results in
some initial testing, we're running more of it.