On 23/04/2020 01:23, Jens Axboe wrote:
> On 4/22/20 4:20 PM, Pavel Begunkov wrote:
>> On 20/04/2020 23:15, Pavel Begunkov wrote:
>>> 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.
>>>
>>
>> Any thoughts on this?
>>
>> I'll return fixing the last timeout bug I saw, but I'd prefer to know
>> on top of what to do that.
>
> I think it's fine, but also likely something that we should defer to
> 5.8. So if there are minor fixes to be done for 5.7, it should be
> arranged as such.
Right, totally agree
--
Pavel Begunkov
