py: Faster qstr search.

Today qstr implementation scans strings sequntially.
In cases there are many strings this can become very inefficient.
This change improves qstr search performance by using binary search in
sorted qstr pools, when possible.

This change introduces an option to create a sorted string pool, which
is then searched by a binary search instead of sequential search.

qstr pool can be either "sorted" or "unsorted", whereas the unsorted is
searched sequentally as today.
Native modules (MP_ROM_QSTR) and frozen modules generate sorted pools.
Currently runtime strings are unsorted.

The constant string pools is split into two and a new pool is introduced,
"special_const_pool". This is required because the first sequence of
strings already requires special ordering therefore created unsorted,
while the rest of the constants are generated sorted.

qstr_find_strn searches strings in each pool. If the pool is sorted and
larger than a threshold, it will be search using binary search instead
of sequential search, significantly improving performance.

py/makeqstrdata.py

@@ -350,14 +350,23 @@ def print_qstr_data(qcfgs, qstrs):
 
     # add NULL qstr with no hash or data
     print(
-        'QDEF(MP_QSTRnull, (const byte*)"%s%s" "")'
+        'QDEF0(MP_QSTRnull, (const byte*)"%s%s" "")'
         % ("\\x00" * cfg_bytes_hash, "\\x00" * cfg_bytes_len)
     )
 
-    # go through each qstr and print it out
-    for order, ident, qstr in sorted(qstrs.values(), key=lambda x: x[0]):
+    # split qstr values into two pools. static consts first.
+    q0_values = [q for q in qstrs.values() if q[0] < 0]
+    q1_values = [q for q in qstrs.values() if q[0] >= 0]
+
+    # go through each qstr in pool 0 and print it out. pool0 has special sort.
+    for order, ident, qstr in sorted(q0_values, key=lambda x: x[0]):
+        qbytes = make_bytes(cfg_bytes_len, cfg_bytes_hash, qstr)
+        print("QDEF0(MP_QSTR_%s, %s)" % (ident, qbytes))
+
+    # go through each qstr in pool 1 and print it out. pool1 is regularly sorted.
+    for order, ident, qstr in sorted(q1_values, key=lambda x: x[2]):
         qbytes = make_bytes(cfg_bytes_len, cfg_bytes_hash, qstr)
-        print("QDEF(MP_QSTR_%s, %s)" % (ident, qbytes))
+        print("QDEF1(MP_QSTR_%s, %s)" % (ident, qbytes))
 
 
 def do_work(infiles):

py/qstr.c

@@ -100,16 +100,38 @@ mp_uint_t qstr_compute_hash(const byte *data, size_t len) {
     return hash;
 }
 
+const qstr_pool_t mp_qstr_special_const_pool = {
+    NULL,                        // no previous pool
+    0,                           // no previous pool
+    MICROPY_ALLOC_QSTR_ENTRIES_INIT,
+    MP_QSTRspecial_const_number_of + 1, // corresponds to number of strings in array just below
+    false,                       // special constant qstrs are not sorted
+    {
+        #ifndef NO_QSTR
+#define QDEF0(id, str) str,
+#define QDEF1(id, str)
+        #include "genhdr/qstrdefs.generated.h"
+#undef QDEF0
+#undef QDEF1
+        #endif
+        (const byte *)"",       // spacer for MP_QSTRspecial_const_number_of
+    },
+};
+
 const qstr_pool_t mp_qstr_const_pool = {
-    NULL,               // no previous pool
-    0,                  // no previous pool
+    (qstr_pool_t *)&mp_qstr_special_const_pool,
+    MP_QSTRspecial_const_number_of + 1,
     MICROPY_ALLOC_QSTR_ENTRIES_INIT,
-    MP_QSTRnumber_of,   // corresponds to number of strings in array just below
+    MP_QSTRnumber_of -
+    (MP_QSTRspecial_const_number_of + 1),      // corresponds to number of strings in array just below
+    true,                               // constant qstrs are sorted
     {
         #ifndef NO_QSTR
-#define QDEF(id, str) str,
+#define QDEF0(id, str)
+#define QDEF1(id, str) str,
         #include "genhdr/qstrdefs.generated.h"
-#undef QDEF
+#undef QDEF0
+#undef QDEF1
         #endif
     },
 };
@@ -160,6 +182,7 @@ STATIC qstr qstr_add(const byte *q_ptr) {
         pool->total_prev_len = MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len;
         pool->alloc = new_alloc;
         pool->len = 0;
+        pool->sorted = false;
         MP_STATE_VM(last_pool) = pool;
         DEBUG_printf("QSTR: allocate new pool of size %d\n", MP_STATE_VM(last_pool)->alloc);
     }
@@ -171,14 +194,48 @@ STATIC qstr qstr_add(const byte *q_ptr) {
     return MP_STATE_VM(last_pool)->total_prev_len + MP_STATE_VM(last_pool)->len - 1;
 }
 
+#define MP_QSTR_SEARCH_THRESHOLD 10
+
 qstr qstr_find_strn(const char *str, size_t str_len) {
-    // work out hash of str
     mp_uint_t str_hash = qstr_compute_hash((const byte *)str, str_len);
 
     // search pools for the data
     for (qstr_pool_t *pool = MP_STATE_VM(last_pool); pool != NULL; pool = pool->prev) {
-        for (const byte **q = pool->qstrs, **q_top = pool->qstrs + pool->len; q < q_top; q++) {
-            if (Q_GET_HASH(*q) == str_hash && Q_GET_LENGTH(*q) == str_len && memcmp(Q_GET_DATA(*q), str, str_len) == 0) {
+        size_t low = 0;
+        size_t high = pool->len - 1;
+
+        // binary search inside the pool
+        if (pool->sorted) {
+            while (high - low > MP_QSTR_SEARCH_THRESHOLD) {
+                size_t mid = (low + high + 1) / 2;
+                const byte **q = pool->qstrs + mid;
+                size_t len = Q_GET_LENGTH(*q);
+                if (len > str_len) {
+                    len = str_len;
+                }
+                int cmp = memcmp(Q_GET_DATA(*q), str, str_len);
+                if (cmp < 0) {
+                    low = mid;
+                } else if (cmp > 0) {
+                    high = mid;
+                } else {
+                    if (Q_GET_LENGTH(*q) < str_len) {
+                        low = mid;
+                    } else if (Q_GET_LENGTH(*q) > str_len) {
+                        high = mid;
+                    } else {
+                        return pool->total_prev_len + (q - pool->qstrs);
+                    }
+                }
+            }
+        }
+
+        // sequential search for the remaining strings
+        for (const byte **q = pool->qstrs + low; q != pool->qstrs + high + 1; q++) {
+            if (*q &&
+                Q_GET_HASH(*q) == str_hash &&
+                Q_GET_LENGTH(*q) == str_len &&
+                memcmp(Q_GET_DATA(*q), str, str_len) == 0) {
                 return pool->total_prev_len + (q - pool->qstrs);
             }
         }

py/qstr.h

@@ -38,9 +38,21 @@
 // first entry in enum will be MP_QSTRnull=0, which indicates invalid/no qstr
 enum {
     #ifndef NO_QSTR
-#define QDEF(id, str) id,
+
+#define QDEF0(id, str) id,
+#define QDEF1(id, str)
     #include "genhdr/qstrdefs.generated.h"
-#undef QDEF
+#undef QDEF0
+#undef QDEF1
+
+    MP_QSTRspecial_const_number_of, // no underscore so it can't clash with any of the above
+
+#define QDEF0(id, str)
+#define QDEF1(id, str) id,
+    #include "genhdr/qstrdefs.generated.h"
+#undef QDEF0
+#undef QDEF1
+
     #endif
     MP_QSTRnumber_of, // no underscore so it can't clash with any of the above
 };
@@ -52,6 +64,7 @@ typedef struct _qstr_pool_t {
     size_t total_prev_len;
     size_t alloc;
     size_t len;
+    bool sorted;
     const byte *qstrs[];
 } qstr_pool_t;
 

tools/makemanifest.py

@@ -354,7 +354,7 @@ def main():
             b'#include "py/emitglue.h"\n'
             b"extern const qstr_pool_t mp_qstr_const_pool;\n"
             b"const qstr_pool_t mp_qstr_frozen_const_pool = {\n"
-            b"    (qstr_pool_t*)&mp_qstr_const_pool, MP_QSTRnumber_of, 0, 0\n"
+            b"    (qstr_pool_t*)&mp_qstr_const_pool, MP_QSTRnumber_of, 0, false, 0\n"
             b"};\n"
             b'const char mp_frozen_mpy_names[1] = {"\\0"};\n'
             b"const mp_raw_code_t *const mp_frozen_mpy_content[1] = {NULL};\n"

tools/mpy-tool.py

@@ -815,7 +815,7 @@ def freeze_mpy(base_qstrs, raw_codes):
         if q is None or q.qstr_esc in base_qstrs or q.qstr_esc in new:
             continue
         new[q.qstr_esc] = (len(new), q.qstr_esc, q.str)
-    new = sorted(new.values(), key=lambda x: x[0])
+    new = sorted(new.values(), key=lambda x: x[2])
 
     print('#include "py/mpconfig.h"')
     print('#include "py/objint.h"')
@@ -871,6 +871,7 @@ def freeze_mpy(base_qstrs, raw_codes):
     print("    MP_QSTRnumber_of, // previous pool size")
     print("    %u, // allocated entries" % qstr_pool_alloc)
     print("    %u, // used entries" % len(new))
+    print("    true, // entries are sorted")
     print("    {")
     for _, _, qstr in new:
         print(