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core: use 64 bit head+tail pointers in fair_queue #11

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merged 1 commit into from
Sep 1, 2021
Merged

core: use 64 bit head+tail pointers in fair_queue #11

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7 changes: 3 additions & 4 deletions include/seastar/core/fair_queue.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -93,11 +93,11 @@ public:
};

class fair_group_rover {
uint32_t _weight = 0;
uint32_t _size = 0;
uint64_t _weight = 0;
uint64_t _size = 0;

public:
fair_group_rover(uint32_t weight, uint32_t size) noexcept;
fair_group_rover(uint64_t weight, uint64_t size) noexcept;

/*
* For both dimentions checks if the current rover is ahead of the
Expand Down Expand Up @@ -175,7 +175,6 @@ using priority_class_ptr = lw_shared_ptr<priority_class>;
/// the given time frame exceeds the disk throughput.
class fair_group {
using fair_group_atomic_rover = std::atomic<fair_group_rover>;
static_assert(fair_group_atomic_rover::is_always_lock_free);

fair_group_atomic_rover _capacity_tail;
fair_group_atomic_rover _capacity_head;
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9 changes: 6 additions & 3 deletions src/core/fair_queue.cc
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Expand Up @@ -81,14 +81,17 @@ std::ostream& operator<<(std::ostream& os, fair_queue_ticket t) {
return os << t._weight << ":" << t._size;
}

fair_group_rover::fair_group_rover(uint32_t weight, uint32_t size) noexcept
fair_group_rover::fair_group_rover(uint64_t weight, uint64_t size) noexcept
: _weight(weight)
, _size(size)
{}

fair_queue_ticket fair_group_rover::maybe_ahead_of(const fair_group_rover& other) const noexcept {
return fair_queue_ticket(std::max<int32_t>(_weight - other._weight, 0),
std::max<int32_t>(_size - other._size, 0));

uint64_t weight_d = std::clamp<int64_t>(_weight - other._weight, 0, std::numeric_limits<int32_t>::max());
uint64_t size_d = std::clamp<int64_t>(_size - other._size, 0, std::numeric_limits<int32_t>::max());

return fair_queue_ticket(weight_d, size_d);
}

fair_group_rover fair_group_rover::operator+(fair_queue_ticket t) const noexcept {
Expand Down