Re: Poll ring behavior broken by f0c5c54945ae92a00cdbb43bdf3abaeab6bd3a23

[Glauber Costa <glauber.costa@datadoghq.com>]

On Thu, Aug 20, 2020 at 11:42 PM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 8/20/20 8:24 PM, Glauber Costa wrote:
> > On Thu, Aug 20, 2020 at 9:57 PM Jens Axboe <axboe@kernel.dk> wrote:
> >>
> >> On 8/20/20 6:46 PM, Glauber Costa wrote:
> >>> I have just noticed that the commit in $subject broke the behavior I
> >>> introduced in
> >>> bf3aeb3dbbd7f41369ebcceb887cc081ffff7b75
> >>>
> >>> In this commit, I have explained why and when it does make sense to
> >>> enter the ring if there are no sqes to submit.
> >>>
> >>> I guess one could argue that in that case one could call the system
> >>> call directly, but it is nice that the application didn't have to
> >>> worry about that, had to take no conditionals, and could just rely on
> >>> io_uring_submit as an entry point.
> >>>
> >>> Since the author is the first to say in the patch that the patch may
> >>> not be needed, my opinion is that not only it is not needed but in
> >>> fact broke applications that relied on previous behavior on the poll
> >>> ring.
> >>>
> >>> Can we please revert?
> >>
> >> Yeah let's just revert it for now. Any chance you can turn this into
> >> a test case for liburing? Would help us not break this in the future.
> >
> > would be my pleasure.
> >
> > Biggest issue is that poll mode really only works with ext4 and xfs as
> > far as I know. That may mean it won't get as much coverage, but maybe
> > that's not relevant.
>
> And raw nvme too, of course. But I'd say coverage is pretty decent with
> those two, in reality that's most likely what people would use for
> polling anyway. So not too concerned about that, and it'll hit multiple
> items in my test suite.
>
> I reverted the change manually, it didn't revert cleanly. Please test
> current -git, thanks!
>

Just tested (through a new unit test) and it works, thanks.

I wrote a unit test that works on HEAD but not on HEAD^.

However you will have to excuse my lack of manners, but in my new work account I
can't have app passwords for GSuite so I am unable to git-send-email
it without talking
to a host of corporate IT people... I'll have to send a ... urgh... PR


> --
> Jens Axboe
>