On 20/04/2020 23:12, Pavel Begunkov wrote:
> On 20/04/2020 22:40, Jens Axboe wrote:
>> On 4/18/20 11:20 AM, Pavel Begunkov wrote:
>>> +static void __io_flush_timeouts(struct io_ring_ctx *ctx)
>>> +{
>>> + u32 end, start;
>>> +
>>> + start = end = ctx->cached_cq_tail;
>>> + do {
>>> + struct io_kiocb *req = list_first_entry(&ctx->timeout_list,
>>> + struct io_kiocb, list);
>>> +
>>> + if (req->flags & REQ_F_TIMEOUT_NOSEQ)
>>> + break;
>>> + /*
>>> + * multiple timeouts may have the same target,
>>> + * check that @req is in [first_tail, cur_tail]
>>> + */
>>> + if (!io_check_in_range(req->timeout.target_cq, start, end))
>>> + break;
>>> +
>>> + list_del_init(&req->list);
>>> + io_kill_timeout(req);
>>> + end = ctx->cached_cq_tail;
>>> + } while (!list_empty(&ctx->timeout_list));
>>> +}
>>> +
>>> static void io_commit_cqring(struct io_ring_ctx *ctx)
>>> {
>>> struct io_kiocb *req;
>>>
>>> - while ((req = io_get_timeout_req(ctx)) != NULL)
>>> - io_kill_timeout(req);
>>> + if (!list_empty(&ctx->timeout_list))
>>> + __io_flush_timeouts(ctx);
>>>
>>> __io_commit_cqring(ctx);
>>>
>>
>> Any chance we can do this without having to iterate timeouts on the
>> completion path?
>>
>
> If you mean the one in __io_flush_timeouts(), then no, unless we forbid timeouts
> with identical target sequences + some extra constraints. The loop there is not
> new, it iterates only over timeouts, that need to be completed, and removes
> them. That's amortised O(1).
We can think about adding unlock/lock, if that's what you are thinking about.
> On the other hand, there was a loop in io_timeout_fn() doing in total O(n^2),
> and it was killed by this patch.
--
Pavel Begunkov
