[dmclock] reservation tag may be wrongly reduced

[dmclock] reservation tag may be wrongly reduced

[Xiangyang Yu]

Hi cephers,
I have read the dmclock paper  and now I am reviewing the dmclock code.

When  a request is popped by a proportion tag ., then the reservation
tag need to reduceed. In my opinion, we only need to reduce by 1/r
in mclock or dmclock. （r is the  reservation inc ）

In the ceph dmclock code, I find that reduced num is max (1, tag.rho),
I think it's wrong .  Code is showed as follows:

// data_mtx should be held when called
void reduce_reservation_tags(ImmediateTagCalc imm, ClientRec& client,
const RequestTag& tag) {
double res_offset =
client.info->reservation_inv * std::max(uint32_t(1), tag.rho);
for (auto& r : client.requests) {
r.tag.reservation -= res_offset;
}
}

If i have missed some information, please tell me.
thanks .