llama : remove KV cache defragmentation logic (#15473)

ggml-ci

src/llama-context.cpp

@@ -39,7 +39,6 @@ llama_context::llama_context(
     cparams.yarn_attn_factor = params.yarn_attn_factor;
     cparams.yarn_beta_fast   = params.yarn_beta_fast;
     cparams.yarn_beta_slow   = params.yarn_beta_slow;
-    cparams.defrag_thold     = params.defrag_thold;
     cparams.embeddings       = params.embeddings;
     cparams.offload_kqv      = params.offload_kqv;
     cparams.flash_attn       = params.flash_attn;
@@ -978,7 +977,7 @@ int llama_context::decode(const llama_batch & batch_inp) {
 
     bool did_optimize = false;
 
-    // handle any pending defrags/shifts
+    // handle any pending shifts/copies
     memory_update(false);
 
     llama_memory_context_ptr mctx;

src/llama-cparams.h

@@ -24,7 +24,6 @@ struct llama_cparams {
     float yarn_attn_factor;
     float yarn_beta_fast;
     float yarn_beta_slow;
-    float defrag_thold;
 
     bool embeddings;
     bool causal_attn;

src/llama-kv-cache.cpp

@@ -525,39 +525,11 @@ llama_memory_context_ptr llama_kv_cache::init_full() {
 }
 
 llama_memory_context_ptr llama_kv_cache::init_update(llama_context * lctx, bool optimize) {
+    GGML_UNUSED(optimize);
+
     bool do_shift = get_has_shift();
 
-    defrag_info dinfo;
-
-    // see if we need to defrag
-    if (n_stream == 1) {
-        // note : for now do not consider defrag for n_stream > 1
-        const auto & cells = v_cells[seq_to_stream[0]];
-
-        bool do_defrag = optimize;
-
-        const auto thold = lctx->get_cparams().defrag_thold;
-
-        if (!do_defrag && thold > 0.0f) {
-            const auto n_kv = cells.used_max_p1();
-
-            // - do not defrag small contexts (i.e. < 2048 tokens)
-            // - count the padding towards the number of used tokens
-            const float fragmentation = n_kv >= 2048 ? std::max(0.0f, 1.0f - (float(cells.get_used() + n_pad)/n_kv)) : 0.0f;
-
-            if (fragmentation > thold) {
-                LLAMA_LOG_DEBUG("%s: fragmentation: %.2f - requesting defrag\n", __func__, fragmentation);
-
-                do_defrag = true;
-            }
-        }
-
-        if (do_defrag) {
-            dinfo = defrag_prepare(lctx->graph_max_nodes());
-        }
-    }
-
-    return std::make_unique<llama_kv_cache_context>(this, lctx, do_shift, std::move(dinfo), std::move(sc_info));
+    return std::make_unique<llama_kv_cache_context>(this, lctx, do_shift, std::move(sc_info));
 }
 
 llama_kv_cache::slot_info_vec_t llama_kv_cache::prepare(const std::vector<llama_ubatch> & ubatches) {
@@ -629,7 +601,7 @@ llama_kv_cache::slot_info_vec_t llama_kv_cache::prepare(const std::vector<llama_
     return res;
 }
 
-bool llama_kv_cache::update(llama_context * lctx, bool do_shift, const defrag_info & dinfo, const stream_copy_info & sc_info) {
+bool llama_kv_cache::update(llama_context * lctx, bool do_shift, const stream_copy_info & sc_info) {
     bool updated = false;
 
     auto * sched = lctx->get_sched();
@@ -699,53 +671,6 @@ bool llama_kv_cache::update(llama_context * lctx, bool do_shift, const defrag_in
         }
     }
 
-    if (!dinfo.empty()) {
-        LLAMA_LOG_DEBUG("%s: defragmenting KV cache\n", __func__);
-
-        // note: for now do not consider defrag for n_stream > 1
-        auto & cells = v_cells[seq_to_stream[0]];
-        auto & head  = v_heads[seq_to_stream[0]];
-
-        // apply moves:
-        {
-            const auto n_kv = dinfo.ids.size();
-
-            for (uint32_t i = 0; i < n_kv; ++i) {
-                assert(dinfo.ids[i] <= n_kv);
-
-                if (dinfo.ids[i] == n_kv || dinfo.ids[i] == i) {
-                    continue;
-                }
-
-                cells.mv(i, dinfo.ids[i]);
-            }
-
-            // reset the head so we can find the first free slot during the next ubatch
-            head = 0;
-        }
-
-        ggml_backend_sched_reset(sched);
-
-        auto * res = lctx->get_gf_res_reserve();
-
-        res->reset();
-
-        auto * gf = build_graph_defrag(res, lctx, dinfo);
-        if (!ggml_backend_sched_alloc_graph(sched, gf)) {
-            LLAMA_LOG_ERROR("%s: failed to allocate compute graph for defrag\n", __func__);
-            return updated;
-        }
-
-        res->set_inputs(nullptr);
-
-        if (lctx->graph_compute(gf, false) != GGML_STATUS_SUCCESS) {
-            LLAMA_LOG_ERROR("%s: failed to compute defrag\n", __func__);
-            return updated;
-        }
-
-        updated = true;
-    }
-
     return updated;
 }
 
@@ -1525,283 +1450,6 @@ ggml_cgraph * llama_kv_cache::build_graph_shift(llm_graph_result * res, llama_co
     return gf;
 }
 
-ggml_cgraph * llama_kv_cache::build_graph_defrag(
-         llm_graph_result * res,
-            llama_context * lctx,
-        const defrag_info & dinfo) const {
-    auto * ctx = res->get_ctx();
-    auto * gf  = res->get_gf();
-
-    GGML_ASSERT(n_stream == 1 && "n_stream > 1 does not support defrag");
-
-    const auto & cells = v_cells[0];
-
-    const auto & ids = dinfo.ids;
-
-    const auto & cparams = lctx->get_cparams();
-
-#if 0
-    // CPU defrag
-    //
-    // TODO: optimizations are possible:
-    //       - multiple threads
-    //       - avoid copying to the host memory when already there
-    //
-    // likely not worth the effort, as we have ggml_graph based defrag
-    //
-
-    const uint32_t n_embd_k_gqa = hparams.n_embd_k_gqa();
-    const uint32_t n_embd_v_gqa = hparams.n_embd_v_gqa();
-
-    const uint32_t kv_size = size;
-
-    std::vector<uint8_t> buf_k;
-    std::vector<uint8_t> buf_v;
-
-    for (uint32_t il = 0; il < n_layer; ++il) {
-        const size_t k_size_row = ggml_row_size(k_l[il]->type, n_embd_k_gqa);
-        const size_t k_size     = ggml_row_size(k_l[il]->type, n_embd_k_gqa*kv_size);
-
-        const size_t v_size_el = ggml_type_size(v_l[il]->type);
-        const size_t v_size    = ggml_row_size (v_l[il]->type, n_embd_v_gqa*kv_size);
-
-        buf_k.resize(k_size);
-        buf_v.resize(v_size);
-
-        ggml_backend_tensor_get(k_l[il], buf_k.data(), 0, buf_k.size());
-        ggml_backend_tensor_get(v_l[il], buf_v.data(), 0, buf_v.size());
-
-        // batch move [i, i+nm) to [id, id+nm)
-        // note: cells can move only to a lower index
-        for (uint32_t i = 0; i < n_kv; ++i) {
-            const uint32_t id = ids[i];
-
-            if (i == id || id == n_kv) {
-                continue;
-            }
-
-            uint32_t nm = 1;
-
-            while (i + nm < n_kv && ids[i + nm] == id + nm) {
-                nm++;
-            }
-
-            // move keys
-            {
-                const int64_t os =  i*k_size_row;
-                const int64_t od = id*k_size_row;
-
-                memcpy(buf_k.data() + od, buf_k.data() + os, nm*k_size_row);
-            }
-
-            // move values (note: they are transposed)
-            {
-                const int64_t os =  i;
-                const int64_t od = id;
-
-                for (uint32_t j = 0; j < n_embd_v_gqa; ++j) {
-                    memcpy(buf_v.data() + (od + j*kv_size)*v_size_el, buf_v.data() + (os + j*kv_size)*v_size_el, nm*v_size_el);
-                }
-            }
-
-            i += nm - 1;
-        }
-
-        ggml_backend_tensor_set(k_l[il], buf_k.data(), 0, buf_k.size());
-        ggml_backend_tensor_set(v_l[il], buf_v.data(), 0, buf_v.size());
-    }
-#else
-    for (uint32_t i = 0; i < ids.size(); ++i) {
-        const uint32_t id = ids[i];
-
-        if (i == id || id == ids.size()) {
-            continue;
-        }
-
-        uint32_t nm = 1;
-
-        while (i + nm < ids.size() && ids[i + nm] == id + nm) {
-            nm++;
-        }
-
-        for (const auto & layer : layers) {
-            const uint32_t il = layer.il;
-
-            const int64_t n_embd_k_gqa = hparams.n_embd_k_gqa(il);
-            const int64_t n_embd_v_gqa = hparams.n_embd_v_gqa(il);
-
-            ggml_tensor * view_k_src = ggml_view_2d(ctx, layer.k,
-                    n_embd_k_gqa, nm,
-                    ggml_row_size(layer.k->type, n_embd_k_gqa),
-                    ggml_row_size(layer.k->type, n_embd_k_gqa*i));
-
-            ggml_tensor * view_k_dst = ggml_view_2d(ctx, layer.k,
-                    n_embd_k_gqa, nm,
-                    ggml_row_size(layer.k->type, n_embd_k_gqa),
-                    ggml_row_size(layer.k->type, n_embd_k_gqa*id));
-
-            ggml_tensor * view_v_src;
-            ggml_tensor * view_v_dst;
-
-            if (cparams.flash_attn) {
-                // NOTE: the V cache is not transposed when using flash attention
-                view_v_src = ggml_view_2d(ctx, layer.v,
-                        n_embd_v_gqa, nm,
-                        ggml_row_size(layer.v->type, n_embd_v_gqa),
-                        ggml_row_size(layer.v->type, n_embd_v_gqa*i));
-
-                view_v_dst = ggml_view_2d(ctx, layer.v,
-                        n_embd_v_gqa, nm,
-                        ggml_row_size(layer.v->type, n_embd_v_gqa),
-                        ggml_row_size(layer.v->type, n_embd_v_gqa*id));
-            } else {
-                view_v_src = ggml_view_2d(ctx, layer.v,
-                        nm, n_embd_v_gqa,
-                        ggml_row_size(layer.v->type, cells.size()),
-                        ggml_row_size(layer.v->type, i));
-
-                view_v_dst = ggml_view_2d(ctx, layer.v,
-                        nm, n_embd_v_gqa,
-                        ggml_row_size(layer.v->type, cells.size()),
-                        ggml_row_size(layer.v->type, id));
-            }
-
-            ggml_build_forward_expand(gf, ggml_cpy(ctx, view_k_src, view_k_dst));
-            ggml_build_forward_expand(gf, ggml_cpy(ctx, view_v_src, view_v_dst));
-        }
-
-        i += nm - 1;
-    }
-
-    //LLAMA_LOG_INFO("gf->n_nodes = %d\n", gf->n_nodes);
-#endif
-
-    return gf;
-}
-
-llama_kv_cache::defrag_info llama_kv_cache::defrag_prepare(int32_t n_max_nodes) const {
-    GGML_ASSERT(n_stream == 1 && "n_stream > 1 does not support defrag");
-
-    const auto & cells = v_cells[0];
-
-    const uint32_t n_layer = layers.size();
-
-    const uint32_t n_kv   = cells.used_max_p1();
-    const uint32_t n_used = cells.get_used();
-
-    assert(n_used <= n_kv);
-
-    //const int64_t t_start = ggml_time_us();
-
-    // number of cells moved
-    uint32_t n_moves = 0;
-
-    // each move requires 6*n_layer tensors (see graph_build_kv_self_defrag)
-    //   - source view, destination view, copy operation
-    //   - x2 for keys and values
-    //const uint32_t max_moves = max_nodes()/(6*n_layer);
-    // TODO: tmp fix https://github.com/ggerganov/llama.cpp/issues/6685#issuecomment-2057579516
-    const uint32_t max_moves = (n_max_nodes - 2*n_layer)/(6*n_layer);
-
-    // determine which KV cells to move where
-    defrag_info res;
-    auto & ids = res.ids;
-
-    ids.resize(n_kv, n_kv);
-
-    for (uint32_t i0 = 0; i0 < n_used; ++i0) {
-        if (!cells.is_empty(i0)) {
-            ids[i0] = i0;
-
-            continue;
-        }
-
-        // found a hole - fill it with data from the end of the cache
-
-        uint32_t nh = 1;
-
-        // determine the size of the hole
-        while (i0 + nh < n_used && cells.is_empty(i0 + nh)) {
-            nh++;
-        }
-
-        uint32_t nf = 0;
-        uint32_t is = n_kv - 1;
-
-        // starting from the end, find nh non-empty cells
-        for (; is > i0; --is) {
-            if (cells.is_empty(is) || ids[is] != n_kv) {
-                continue;
-            }
-
-            // non-empty cell which is not yet moved
-            nf++;
-
-            if (nf == nh) {
-                break;
-            }
-        }
-
-        // this can only happen if `n_used` is not accurate, which would be a bug
-        GGML_ASSERT(nf == nh && "KV defrag bug: nf != nh");
-
-        nf = 0;
-
-        uint32_t i1 = is;
-
-        // are we moving a continuous block of memory?
-        bool cont = false;
-
-        // should we stop searching for the next move?
-        bool stop = false;
-
-        // go back and move the nf cells to the hole
-        for (; i1 < n_kv; ++i1) {
-            if (cells.is_empty(i1) || ids[i1] != n_kv) {
-                if (n_moves == max_moves) {
-                    stop = true;
-                    break;
-                }
-
-                cont = false;
-                continue;
-            }
-
-            // this cell goes to (i0 + nf)
-            ids[i1] = i0 + nf;
-
-            if (!cont) {
-                n_moves++;
-                cont = true;
-            }
-
-            nf++;
-
-            if (nf == nh) {
-                break;
-            }
-        }
-
-        if (stop || n_moves == max_moves) {
-            break;
-        }
-
-        //LLAMA_LOG_INFO("(tmp log) KV defrag: move [%u, %u) to [%u, %u)\n", is, i1 + 1, i0, i0 + nh);
-
-        i0 += nh - 1;
-    }
-
-    if (n_moves == 0) {
-        return {};
-    }
-
-    LLAMA_LOG_DEBUG("%s: (tmp log) KV defrag cell moves: %u\n", __func__, n_moves);
-
-    LLAMA_LOG_DEBUG("%s: expected gf nodes: %u\n", __func__, 6*n_moves*n_layer);
-
-    return res;
-}
-
 bool llama_kv_cache::is_masked_swa(llama_pos p0, llama_pos p1) const {
     assert(p0 >= 0 && p1 >= 0);
 
@@ -2300,9 +1948,8 @@ llama_kv_cache_context::llama_kv_cache_context(
         llama_kv_cache * kv,
         llama_context * lctx,
         bool do_shift,
-        defrag_info dinfo,
-        stream_copy_info sc_info) : status(LLAMA_MEMORY_STATUS_SUCCESS), kv(kv), lctx(lctx), do_shift(do_shift), dinfo(std::move(dinfo)), sc_info(std::move(sc_info)) {
-    if (!do_shift && this->dinfo.empty() && this->sc_info.empty()) {
+        stream_copy_info sc_info) : status(LLAMA_MEMORY_STATUS_SUCCESS), kv(kv), lctx(lctx), do_shift(do_shift), sc_info(std::move(sc_info)) {
+    if (!do_shift && this->sc_info.empty()) {
         status = LLAMA_MEMORY_STATUS_NO_UPDATE;
     }
 }
@@ -2330,7 +1977,7 @@ bool llama_kv_cache_context::apply() {
 
     // no ubatches -> this is a KV cache update
     if (ubatches.empty()) {
-        kv->update(lctx, do_shift, dinfo, sc_info);
+        kv->update(lctx, do_shift, sc_info);
 
         return true;
     }

src/llama-kv-cache.h

@@ -24,17 +24,6 @@ public:
     // this callback is used to filter out layers that should not be included in the cache
     using layer_filter_cb = std::function<bool(int32_t il)>;
 
-    struct defrag_info {
-        bool empty() const {
-            return ids.empty();
-        }
-
-        // contains information about which cell moves where:
-        //  - cell i moves to ids[i]
-        //  - if ids[i] == i || ids[i] == ids.size(), then cell i is not moved
-        std::vector<uint32_t> ids;
-    };
-
     struct stream_copy_info {
         bool empty() const {
             assert(ssrc.size() == sdst.size());
@@ -173,7 +162,7 @@ public:
     // return empty vector on failure
     slot_info_vec_t prepare(const std::vector<llama_ubatch> & ubatches);
 
-    bool update(llama_context * lctx, bool do_shift, const defrag_info & dinfo, const stream_copy_info & sc_info);
+    bool update(llama_context * lctx, bool do_shift, const stream_copy_info & sc_info);
 
     // find a slot of kv cells that can hold the ubatch
     // if cont == true, then the slot must be continuous
@@ -254,9 +243,6 @@ private:
     // model layer id -> KV cache layer id
     std::unordered_map<int32_t, int32_t> map_layer_ids;
 
-    // return non-empty vector if cells have been moved
-    defrag_info defrag_prepare(int32_t n_max_nodes) const;
-
     size_t total_size() const;
 
     size_t size_k_bytes() const;
@@ -277,11 +263,6 @@ private:
                llm_graph_result * res,
                   llama_context * lctx) const;
 
-    ggml_cgraph * build_graph_defrag(
-               llm_graph_result * res,
-                  llama_context * lctx,
-              const defrag_info & dinfo) const;
-
     struct cell_ranges_t {
         uint32_t strm;
 
@@ -299,7 +280,6 @@ class llama_kv_cache_context : public llama_memory_context_i {
 public:
     // some shorthands
     using slot_info_vec_t  = llama_kv_cache::slot_info_vec_t;
-    using defrag_info      = llama_kv_cache::defrag_info;
     using stream_copy_info = llama_kv_cache::stream_copy_info;
 
     // used for errors
@@ -314,7 +294,6 @@ public:
             llama_kv_cache * kv,
             llama_context * lctx,
             bool do_shift,
-            defrag_info dinfo,
             stream_copy_info sc_info);
 
     // used to create a batch procesing context from a batch
@@ -374,8 +353,6 @@ private:
 
     bool do_shift = false;
 
-    defrag_info dinfo;
-
     stream_copy_info sc_info;
 
     //

src/llama-kv-cells.h

@@ -77,24 +77,24 @@ public:
     }
 
     // move cell isrc to idst (used during defrag)
-    void mv(uint32_t isrc, uint32_t idst) {
-        assert(isrc < pos.size());
-        assert(idst < pos.size());
+    //void mv(uint32_t isrc, uint32_t idst) {
+    //    assert(isrc < pos.size());
+    //    assert(idst < pos.size());
 
-        assert(pos[idst] == -1);
-        assert(pos[isrc] != -1);
+    //    assert(pos[idst] == -1);
+    //    assert(pos[isrc] != -1);
 
-        pos  [idst] = pos  [isrc];
-        shift[idst] = shift[isrc];
-        seq  [idst] = seq  [isrc];
+    //    pos  [idst] = pos  [isrc];
+    //    shift[idst] = shift[isrc];
+    //    seq  [idst] = seq  [isrc];
 
-        pos  [isrc] = -1;
-        shift[isrc] =  0;
-        seq  [isrc].reset();
+    //    pos  [isrc] = -1;
+    //    shift[isrc] =  0;
+    //    seq  [isrc].reset();
 
-        used.erase (isrc);
-        used.insert(idst);
-    }
+    //    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 cp(uint32_t i, uint32_t n) const {

src/llama-memory.h

@@ -77,7 +77,7 @@ struct llama_memory_i {
     // simulate full cache, used for allocating worst-case compute buffers
     virtual llama_memory_context_ptr init_full() = 0;
 
-    // prepare for any pending memory updates, such as shifts, defrags, etc.
+    // prepare for any pending memory updates, such as shifts, copies, etc.
     // status == LLAMA_MEMORY_STATUS_NO_UPDATE if there is nothing to update
     virtual llama_memory_context_ptr init_update(llama_context * lctx, bool optimize) = 0;