Re: [PATCH v12 2/2] fuse: add default_request_timeout and max_request_timeout sysctls

Joanne Koong
2025-01-23T23:20:37Z

On Thu, Jan 23, 2025 at 10:40 AM Bernd Schubert
<bernd.schubert@fastmail.fm> wrote:
>
>
>
> On 1/23/25 19:32, Joanne Koong wrote:
> > On Thu, Jan 23, 2025 at 10:06 AM Bernd Schubert
> > <bernd.schubert@fastmail.fm> wrote:
> >>
> >>
> >>
> >> On 1/23/25 18:48, Joanne Koong wrote:
> >>> On Thu, Jan 23, 2025 at 9:19 AM Bernd Schubert
> >>> <bernd.schubert@fastmail.fm> wrote:
> >>>>
> >>>> Hi Joanne,
> >>>>
> >>>>>>> Thanks, applied and pushed with some cleanups including Luis's clamp idea.
> >>>>>>
> >>>>>> Hi Miklos,
> >>>>>>
> >>>>>> I don't think the timeouts do work with io-uring yet, I'm not sure
> >>>>>> yet if I have time to work on that today or tomorrow (on something
> >>>>>> else right now, I can try, but no promises).
> >>>>>
> >>>>> Hi Bernd,
> >>>>>
> >>>>> What are your thoughts on what is missing on the io-uring side for
> >>>>> timeouts? If a request times out, it will abort the connection and
> >>>>> AFAICT, the abort logic should already be fine for io-uring, as users
> >>>>> can currently abort the connection through the sysfs interface and
> >>>>> there's no internal difference in aborting through sysfs vs timeouts.
> >>>>>
> >>>>
> >>>> in fuse_check_timeout() it iterates over each fud and then fpq.
> >>>> In dev_uring.c fpq is is per queue but unrelated to fud. In current
> >>>> fuse-io-uring fud is not cloned anymore - using fud won't work.
> >>>> And Requests are also not queued at all on the other list
> >>>> fuse_check_timeout() is currently checking.
> >>>
> >>> In the io-uring case, there still can be fuds and their associated
> >>> fpqs given that /dev/fuse can be used still, no? So wouldn't the
> >>> io-uring case still need this logic in fuse_check_timeout() for
> >>> checking requests going through /dev/fuse?
> >>
> >> Yes, these need to be additionally checked.
> >>
> >>>
> >>>>
> >>>> Also, with a ring per core, maybe better to use
> >>>> a per queue check that is core bound? I.e. zero locking overhead?
> >>>
> >>> How do you envision a queue check that bypasses grabbing the
> >>> queue->lock? The timeout handler could be triggered on any core, so
> >>> I'm not seeing how it could be core bound.
> >>
> >> I don't want to bypass it, but maybe each queue could have its own
> >> workq and timeout checker? And then use queue_delayed_work_on()?
> >>
> >>
> >>>
> >>>> And I think we can also avoid iterating over hash lists (queue->fpq),
> >>>> but can use the 'ent_in_userspace' list.
> >>>>
> >>>> We need to iterate over these other entry queues anyway:
> >>>>
> >>>> ent_w_req_queue
> >>>> fuse_req_bg_queue
> >>>> ent_commit_queue
> >>>>
> >>>
> >>> Why do we need to iterate through the ent lists (ent_w_req_queue and
> >>> ent_commit_queue)? AFAICT, in io-uring a request is either on the
> >>> fuse_req_queue/fuse_req_bg_queue or on the fpq->processing list. Even
> >>> when an entry has been queued to ent_w_req_queue or ent_commit_queue,
> >>> the request itself is still queued on
> >>> fuse_req_queue/fuse_req_bg_queue/fpq->processing. I'm not sure I
> >>> understand why we still need to look at the ent lists?
> >>
> >> Yeah you are right, we could avoid ent_w_req_queue and ent_commit_queue
> >> if we use fpq->processing, but processing consists of 256 lists -
> >> overhead is much smaller by using the entry lists?
> >>
> >>
> >>>
> >>>>
> >>>> And we also need to iterate over
> >>>>
> >>>> fuse_req_queue
> >>>> fuse_req_bg_queue
> >>>
> >>> Why do we need to iterate through fuse_req_queue and
> >>> fuse_req_bg_queue? fuse_uring_request_expired() checks the head of
> >>> fuse_req_queue and fuse_req_bg_queue and given that requests are added
> >>> to fuse_req_queue/fuse_req_bg_queue sequentially (eg added to the tail
> >>> of these lists), why isn't this enough?
> >>
> >> I admit I'm a bit lost with that question. Aren't you pointing out
> >> the same lists as I do?
> >>
> >
> > Oh, I thought your comment was saying that we need to "iterate" over
> > it (eg go through every request on the lists)? It currently already
> > checks the fuse_req_queue and fuse_req_bg_queue lists (in
> > fuse_uring_request_expired() which gets invoked in the
> > fuse_check_timeout() timeout handler).
> >
> > Maybe the fuse_uring_request_expired() addition got missed - I tried
> > to call this out in the cover letter changelog, as I had to rebase
> > this patchset on top of the io-uring patches, so I added this function
> > in to make it work for io-uring. I believe this suffices for now for
> > the io uring case (with future optimizations that can be added)?
>
>
> Ah sorry, that is me, I had missed you had already rebased it to
> io-uring.
>
> So we are good to land this version.
> Just would be good if we could optimize this soon - our test systems
> have 96 cores - 24576 list heads to check... I won't manage to work
> on it today and probably also not tomorrow, but by Monday I should
> have an optimized version ready.
>

Oh wow, 96 cores!! I'll submit an optimized version of this today or
tomorrow then, if that makes things easier for you.

Thanks,
Joanne

> Thanks,
> Bernd
>