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

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

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.