Re: [Tarantool-patches] [PATCH vshard 10/11] sched: introduce vshard.storage.sched module

[Oleg Babin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi! Thanks for explanation. LGTM.

On 06.03.2021 01:06, Vladislav Shpilevoy wrote:
> Thanks for the review!
>
> On 04.03.2021 22:02, Oleg Babin wrote:
>> Hi! I've looked your patch again. See one comment below.
>>
>> On 23.02.2021 03:15, Vladislav Shpilevoy wrote:
>>> +--
>>> +-- Return the remaining timeout in case there was a yield. This helps to save
>>> +-- current clock get in the caller code if there were no yields.
>>> +--
>>> +local function sched_ref_start(timeout)
>>> +    local deadline = fiber_clock() + timeout
>>> +    local ok, err
>>> +    -- Fast-path. Moves are extremely rare. No need to inc-dec the ref queue
>>> +    -- then nor try to start some loops.
>>> +    if M.move_count == 0 and M.move_queue == 0 then
>>> +        goto success
>>> +    end
>>> +
>>> +    M.ref_queue = M.ref_queue + 1
>>> +
>>> +::retry::
>>> +    if M.move_count > 0 then
>>> +        goto wait_and_retry
>>> +    end
>>> +    -- Even if move count is zero, must ensure the time usage is fair. Does not
>>> +    -- matter in case the moves have no quota at all. That allows to ignore them
>>> +    -- infinitely until all refs end voluntarily.
>>> +    if M.move_queue > 0 and M.ref_strike >= M.ref_quota and
>>> +       M.move_quota > 0 then
>> Is it reasonable to check `move_quota > 0`. According tests it always should be positive.
>>
>> I see similar check for `ref_quota` as well.
> These are special cases covered with tests in unit-tap/scheduler.test.lua
> in test_move_zero_quota() and test_ref_zero_quota().
>
> Zero quota means the operation can be suppressed by the other operation
> infinitely long.