[Python-checkins] bpo-43452: Micro-optimizations to PyType_Lookup (GH-24804)
pablogsal
webhook-mailer at python.org
Sat Mar 20 15:12:14 EDT 2021
https://github.com/python/cpython/commit/ee48c7d54147ae906776b9f6f96e8920e097d0c4
commit: ee48c7d54147ae906776b9f6f96e8920e097d0c4
branch: master
author: Dino Viehland <dinoviehland at fb.com>
committer: pablogsal <Pablogsal at gmail.com>
date: 2021-03-20T19:12:05Z
summary:
bpo-43452: Micro-optimizations to PyType_Lookup (GH-24804)
The common case going through _PyType_Lookup is to have a cache hit. There are some small tweaks that can make this a little cheaper:
* The name field identity is used for a cache hit and is kept alive by the cache. So there's no need to read the hash code o the name - instead, the address can be used as the hash.
* There's no need to check if the name is cachable on the lookup either, it probably is, and if it is, it'll be in the cache.
* If we clear the version tag when invalidating a type then we don't actually need to check for a valid version tag bit.
files:
A Misc/NEWS.d/next/Core and Builtins/2021-03-20-01-21-37.bpo-43452.tDVJkc.rst
M Objects/typeobject.c
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-03-20-01-21-37.bpo-43452.tDVJkc.rst b/Misc/NEWS.d/next/Core and Builtins/2021-03-20-01-21-37.bpo-43452.tDVJkc.rst
new file mode 100644
index 0000000000000..c2fe10afdee8c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2021-03-20-01-21-37.bpo-43452.tDVJkc.rst
@@ -0,0 +1 @@
+Added micro-optimizations to ``_PyType_Lookup()`` to improve cache lookup performance in the common case of cache hits.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 650e4144f1627..2b6ff59e5fd3c 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -32,8 +32,7 @@ class object "PyObject *" "&PyBaseObject_Type"
& ((1 << MCACHE_SIZE_EXP) - 1))
#define MCACHE_HASH_METHOD(type, name) \
- MCACHE_HASH((type)->tp_version_tag, \
- ((PyASCIIObject *)(name))->hash)
+ MCACHE_HASH((type)->tp_version_tag, ((Py_ssize_t)(name)) >> 3)
#define MCACHE_CACHEABLE_NAME(name) \
PyUnicode_CheckExact(name) && \
PyUnicode_IS_READY(name) && \
@@ -338,6 +337,7 @@ PyType_Modified(PyTypeObject *type)
}
}
type->tp_flags &= ~Py_TPFLAGS_VALID_VERSION_TAG;
+ type->tp_version_tag = 0; /* 0 is not a valid version tag */
}
static void
@@ -396,6 +396,7 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {
Py_XDECREF(type_mro_meth);
type->tp_flags &= ~(Py_TPFLAGS_HAVE_VERSION_TAG|
Py_TPFLAGS_VALID_VERSION_TAG);
+ type->tp_version_tag = 0; /* 0 is not a valid version tag */
}
static int
@@ -3351,18 +3352,15 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
PyObject *res;
int error;
- if (MCACHE_CACHEABLE_NAME(name) &&
- _PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
- /* fast path */
- unsigned int h = MCACHE_HASH_METHOD(type, name);
- struct type_cache *cache = get_type_cache();
- struct type_cache_entry *entry = &cache->hashtable[h];
- if (entry->version == type->tp_version_tag && entry->name == name) {
+ unsigned int h = MCACHE_HASH_METHOD(type, name);
+ struct type_cache *cache = get_type_cache();
+ struct type_cache_entry *entry = &cache->hashtable[h];
+ if (entry->version == type->tp_version_tag &&
+ entry->name == name) {
#if MCACHE_STATS
- cache->hits++;
+ cache->hits++;
#endif
- return entry->value;
- }
+ return entry->value;
}
/* We may end up clearing live exceptions below, so make sure it's ours. */
@@ -3385,24 +3383,21 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
return NULL;
}
- if (MCACHE_CACHEABLE_NAME(name)) {
- struct type_cache *cache = get_type_cache();
- if (assign_version_tag(cache, type)) {
- unsigned int h = MCACHE_HASH_METHOD(type, name);
- struct type_cache_entry *entry = &cache->hashtable[h];
- entry->version = type->tp_version_tag;
- entry->value = res; /* borrowed */
- assert(((PyASCIIObject *)(name))->hash != -1);
+ if (MCACHE_CACHEABLE_NAME(name) && assign_version_tag(cache, type)) {
+ h = MCACHE_HASH_METHOD(type, name);
+ struct type_cache_entry *entry = &cache->hashtable[h];
+ entry->version = type->tp_version_tag;
+ entry->value = res; /* borrowed */
+ assert(((PyASCIIObject *)(name))->hash != -1);
#if MCACHE_STATS
- if (entry->name != Py_None && entry->name != name) {
- cache->collisions++;
- }
- else {
- cache->misses++;
- }
-#endif
- Py_SETREF(entry->name, Py_NewRef(name));
+ if (entry->name != Py_None && entry->name != name) {
+ cache->collisions++;
}
+ else {
+ cache->misses++;
+ }
+#endif
+ Py_SETREF(entry->name, Py_NewRef(name));
}
return res;
}
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