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.
--
Jens Axboe
