llama.cpp/src/llama-kv-cells.h

#pragma once

#include "llama.h"
#include "llama-cparams.h"

#include <bitset>
#include <cassert>
#include <vector>
#include <set>
#include <map>

// meta information about KV cells that can be part of multiple sequences at the same time
// TODO: add unit tests
class llama_kv_cells_unified {
public:
    void reset() {
        for (uint32_t i = 0; i < pos.size(); ++i) {
            pos[i]   = -1;
            shift[i] =  0;
            seq[i].reset();
        }

        has_shift = false;

        used.clear();

        for (uint32_t s = 0; s < LLAMA_MAX_SEQ; ++s) {
            seq_pos[s].clear();
        }
    }

    void reset_shift() {
        has_shift = false;

        for (uint32_t i = 0; i < shift.size(); ++i) {
            shift[i] = 0;
        }
    }

    uint32_t size() const {
        return pos.size();
    }

    void resize(uint32_t n) {
        pos.resize(n);
        shift.resize(n);
        seq.resize(n);

        reset();
    }

    bool is_empty(uint32_t i) const {
        assert(i < pos.size());
        assert((pos[i] < 0 && pos[i] == -1) || pos[i] >= 0);

        return pos[i] == -1;
    }

    uint32_t get_used() const {
        return used.size();
    }

    // the index of the first cell that is used
    // return 0 if no cells are used
    uint32_t used_min() const {
        return used.empty() ? 0 : *used.begin();
    }

    // the index of the last cell that is used + 1
    // return 0 if no cells are used
    uint32_t used_max_p1() const {
        return used.empty() ? 0 : *used.rbegin() + 1;
    }

    bool get_has_shift() const {
        return has_shift;
    }

    // move cell isrc to idst (used during defrag)
    void mv(uint32_t isrc, uint32_t idst) {
        assert(isrc < pos.size());
        assert(idst < pos.size());

        assert(pos[idst] == -1);
        assert(pos[isrc] != -1);

        pos  [idst] = pos  [isrc];
        shift[idst] = shift[isrc];
        seq  [idst] = seq  [isrc];

        pos  [isrc] = -1;
        shift[isrc] =  0;
        seq  [isrc].reset();

        used.erase (isrc);
        used.insert(idst);
    }

    // copy the state of cells [i, i + n) (used for save/restore the state of the cells)
    llama_kv_cells_unified cp(uint32_t i, uint32_t n) const {
        assert(i + n <= pos.size());

        llama_kv_cells_unified res;

        res.resize(n);

        for (uint32_t j = 0; j < n; ++j) {
            res.pos[j] = pos[i + j];
            res.seq[j] = seq[i + j];

            assert(shift[i + j] == 0);
        }

        return res;
    }

    // set the state of cells [i, i + other.pos.size()) (used for save/restore the state of the cells)
    void set(uint32_t i, const llama_kv_cells_unified & other) {
        assert(i + other.pos.size() <= pos.size());

        for (uint32_t j = 0; j < other.pos.size(); ++j) {
            if (pos[i + j] == -1 && other.pos[j] != -1) {
                used.insert(i + j);
            }

            if (pos[i + j] != -1 && other.pos[j] == -1) {
                used.erase(i + j);
            }

            if (pos[i + j] != -1) {
                seq_pos_rm(i + j);
            }

            pos[i + j] = other.pos[j];
            seq[i + j] = other.seq[j];

            if (pos[i + j] != -1) {
                seq_pos_add(i + j);
            }

            assert(shift[i + j] == 0);
        }
    }

    // clear a non-empty cell
    void rm(uint32_t i) {
        assert(i < pos.size());
        assert(pos[i] != -1);

        seq_pos_rm(i);
        seq[i].reset();

        pos[i] = -1;
        shift[i] = 0;

        used.erase(i);
    }

    // note: call only if the cell has seq_id
    // return true if the cell becomes empty
    bool seq_rm(uint32_t i, llama_seq_id seq_id) {
        assert(i < pos.size());
        assert(seq[i].test(seq_id));
        assert(pos[i] != -1);
        assert(seq_id >= 0);

        seq[i].reset(seq_id);
        seq_pos_dec(seq_id, pos[i]);

        if (seq[i].none()) {
            pos[i] = -1;
            shift[i] = 0;

            used.erase(i);

            return true;
        }

        return false;
    }

    // return true if the cell becomes empty (i.e. it did not contain seq_id before the call)
    bool seq_keep(uint32_t i, llama_seq_id seq_id) {
        assert(i < pos.size());

        if (seq[i].test(seq_id)) {
            seq_pos_rm(i);
            seq[i].reset();

            seq[i].set(seq_id);
            seq_pos_inc(seq_id, pos[i]);

            return false;
        }

        if (seq[i].any()) {
            seq_pos_rm(i);
            seq[i].reset();

            pos[i] = -1;
            shift[i] = 0;

            used.erase(i);

            return true;
        }

        assert(pos[i] == -1);

        return false;
    }

    // number of different sequences in the cell
    int seq_count(uint32_t i) const {
        assert(i < pos.size());
        assert(pos[i] != -1);

        return seq[i].count();
    }

    // check if the cell contains seq_id
    bool seq_has(uint32_t i, llama_seq_id seq_id) const {
        assert(i < pos.size());
        assert(seq_id >= 0);

        return seq[i].test(seq_id);
    }

    // note: call only if the cell is not empty and the seq_id is not in the cell
    void seq_add(uint32_t i, llama_seq_id seq_id) {
        assert(i < pos.size());
        assert(pos[i] != -1);
        assert(!seq[i].test(seq_id));

        seq[i].set(seq_id);
        seq_pos_inc(seq_id, pos[i]);
    }

    // return the sequence id of this cell
    // note: call only for cells with exactly one sequence
    llama_seq_id seq_get(uint32_t i) const {
        assert(seq[i].count() == 1);

        for (int s = 0; s < LLAMA_MAX_SEQ; ++s) {
            if (seq[i].test(s)) {
                return s;
            }
        }

        return -1;
    }

    // the minimum position of sequence seq_id currently present in any of the cells
    // return -1 if the sequence is not present
    llama_pos seq_pos_min(llama_seq_id seq_id) const {
        assert(seq_id >= 0);
        assert(seq_id < LLAMA_MAX_SEQ);

        if (seq_pos[seq_id].empty()) {
            return -1;
        }

        assert(seq_pos[seq_id].begin()->second > 0);

        return seq_pos[seq_id].begin()->first;
    }

    // the maximum position of sequence seq_id currently present in any of the cells
    // return -1 if the sequence is not present
    llama_pos seq_pos_max(llama_seq_id seq_id) const {
        assert(seq_id >= 0);
        assert(seq_id < LLAMA_MAX_SEQ);

        if (seq_pos[seq_id].empty()) {
            return -1;
        }

        assert(seq_pos[seq_id].rbegin()->second > 0);

        return seq_pos[seq_id].rbegin()->first;
    }

    // note: call only if the cell is not empty
    llama_pos pos_get(uint32_t i) const {
        assert(i < pos.size());
        assert(pos[i] != -1);

        return pos[i];
    }

    // note: call only if the cell is not empty
    llama_pos get_shift(uint32_t i) const {
        assert(i < pos.size());
        assert(pos[i] != -1);

        return shift[i];
    }

    // check if a cell is not empty and its position is within [p0, p1)
    bool pos_in(uint32_t i, llama_pos p0, llama_pos p1) const {
        assert(i < pos.size());

        return pos[i] >= p0 && pos[i] < p1;
    }

    // set the position of an empty cell
    // does not modify "has_shift"
    // note: call only if the cell is empty
    void pos_set(uint32_t i, llama_pos p) {
        assert(i < pos.size());
        assert(pos[i] == -1);
        assert(seq[i].none());

        pos[i] = p;

        used.insert(i);
    }

    // pos[i] = pos[i] + d
    // sets "has_shift" to true
    // note: call only if the cell is not empty
    bool pos_add(uint32_t i, llama_pos d) {
        assert(i < pos.size());
        assert(pos[i] != -1);

        seq_pos_rm(i);

        pos[i]   += d;
        shift[i] += d;

        has_shift = true;

        if (pos[i] < 0) {
            seq[i].reset();
            pos[i] = -1;
            shift[i] = 0;

            used.erase(i);

            return true;
        }

        seq_pos_add(i);

        return false;
    }

    // pos[i] = pos[i] / d
    // sets "has_shift" to true
    // note: call only if the cell is not empty
    void pos_div(uint32_t i, int d) {
        assert(i < pos.size());
        assert(pos[i] != -1);

        const llama_pos p_old = pos[i];

        seq_pos_rm(i);

        pos[i]   /= d;
        shift[i] += p_old - pos[i];

        seq_pos_add(i);

        has_shift = true;
    }

private:
    bool has_shift = false;

    // set of indices of used cells (i.e. pos[i] != -1, allowed to not have any seq_id)
    std::set<uint32_t> used;

    std::vector<llama_pos> pos;

    // this array accumulates any applied shifts to the pos array since the last reset_shift() call
    // this is used to queue multiple updates to the pos array, which in the end can be applied in one go:
    //
    //   cells.pos_add(x, shift_x);
    //   cells.pos_div(y, shift_y);
    //   ...
    //
    //   if (cells.has_shift()) {
    //      for (int i = 0; i < n; ++i) {
    //          auto shift_i = cells.get_shift(i);
    //          ...
    //      }
    //      cells.reset_shift();
    //   }
    //
    std::vector<llama_pos> shift;

    using seq_set_t = std::bitset<LLAMA_MAX_SEQ>;

    // the bitset seq[i] tells us which sequences are currently occupying the i-th cell
    std::vector<seq_set_t> seq;

    // the set seq_pos[s][p] tells us how many times the position p is currently present for sequence s
    // if the position p is not present, seq_pos[s][p] is not set
    // this way seq_pos[s].begin() and seq_pos[s].rbegin() give us the min/max positions currently in the cache
    //
    // note that we cannot a use an std::set because in some cases a position can occur more than once for the same seq:
    //  - during performing a cache reuse via (rm + add)
    //  - some vision models have input embeddings with repeating positions
    //
    std::map<llama_pos, int> seq_pos[LLAMA_MAX_SEQ];

    // helper functions for updating `seq_pos`, once cell at a time:

    void seq_pos_dec(llama_seq_id s, llama_pos p) {
        auto it = seq_pos[s].find(p);
        assert(it != seq_pos[s].end());

        if (--it->second == 0) {
            seq_pos[s].erase(it);
        }
    }

    void seq_pos_inc(llama_seq_id s, llama_pos p) {
        seq_pos[s][p]++;
    }

    // remove cell i
    void seq_pos_rm(uint32_t i) {
        for (int s = 0; s < LLAMA_MAX_SEQ; ++s) {
            if (seq[i].test(s)) {
                seq_pos_dec(s, pos[i]);
            }
        }
    }

    // add cell i
    void seq_pos_add(uint32_t i) {
        for (int s = 0; s < LLAMA_MAX_SEQ; ++s) {
            if (seq[i].test(s)) {
                seq_pos_inc(s, pos[i]);
            }
        }
    }
};