On 9/24/19 3:49 AM, Peter Zijlstra wrote:
> On Tue, Sep 24, 2019 at 10:36:28AM +0200, Jens Axboe wrote:
>
>> +struct io_wait_queue {
>> + struct wait_queue_entry wq;
>> + struct io_ring_ctx *ctx;
>> + struct task_struct *task;
>
> wq.private is where the normal waitqueue stores the task pointer.
>
> (I'm going to rename that)
If you do that, then we can just base the io_uring parts on that.
>> + unsigned to_wait;
>> + unsigned nr_timeouts;
>> +};
>> +
>> +static inline bool io_should_wake(struct io_wait_queue *iowq)
>> +{
>> + struct io_ring_ctx *ctx = iowq->ctx;
>> +
>> + /*
>> + * Wake up if we have enough events, or if a timeout occured since we
>> + * started waiting. For timeouts, we always want to return to userspace,
>> + * regardless of event count.
>> + */
>> + return io_cqring_events(ctx->rings) >= iowq->to_wait ||
>> + atomic_read(&ctx->cq_timeouts) != iowq->nr_timeouts;
>> +}
>> +
>> +static int io_wake_function(struct wait_queue_entry *curr, unsigned int
>> mode,
>> + int wake_flags, void *key)
>> +{
>> + struct io_wait_queue *iowq = container_of(curr, struct io_wait_queue,
>> + wq);
>> +
>> + if (io_should_wake(iowq)) {
>> + list_del_init(&curr->entry);
>> + wake_up_process(iowq->task);
>
> Then you can use autoremove_wake_function() here.
>
>> + return 1;
>> + }
>> +
>> + return -1;
>> +}
>
> Ideally we'd get wait_event()'s @cond in a custom wake function. Then we
> can _always_ do this.
>
> This is one I'd love to have lambda functions for. It would actually
> work with GCC nested functions, because the wake function will always be
> in scope, but we can't use those in the kernel for other reasons :/
I'll be happy enough if I can just call autoremove_wake_function(), I
think that will simplify the case enough for io_uring to not really make
me care too much about going further. I'll leave that to you, if you
have the desire :-)
--
Jens Axboe
