From: Vladimír Čunát <vladimir.cunat@nic.cz>
Date: Wed, 7 Aug 2019 07:36:13 +0000 (+0200)
Subject: lua FFI: avoid frequent usage of lua_pushpointer()
X-Git-Tag: v4.3.0~4^2~4
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=3647106a9c45a115477bd8a1060edcbc687f8da4;p=thirdparty%2Fknot-resolver.git

lua FFI: avoid frequent usage of lua_pushpointer()

The new way of transitioning to layer callbacks - done because of
portability (mainly to aarch64) - is a bit expensive.  This is a simple
way of recovering that cost.  Merge 603a24f regressed speed a bit.
---

diff --git a/daemon/ffimodule.c b/daemon/ffimodule.c
index 24f6aaccd..c1cb50e98 100644
--- a/daemon/ffimodule.c
+++ b/daemon/ffimodule.c
@@ -126,6 +126,8 @@ static int l_ffi_deinit(struct kr_module *module)
 	return ret;
 }
 
+kr_layer_t kr_layer_t_static;
+
 /** @internal Helper for calling a layer Lua function by e.g. SLOT_begin. */
 static int l_ffi_call_layer(kr_layer_t *ctx, int slot_ix)
 {
@@ -135,8 +137,11 @@ static int l_ffi_call_layer(kr_layer_t *ctx, int slot_ix)
 	lua_State *L = the_worker->engine->L;
 	lua_rawgeti(L, LUA_REGISTRYINDEX, wrap_slot);
 	lua_rawgeti(L, LUA_REGISTRYINDEX, cb_slot);
-	lua_pushpointer(L, ctx);
-	const int ret = l_ffi_call_mod(L, 2);
+	/* We pass the content of *ctx via a global structure to avoid
+	 * lua (full) userdata, as that's relatively expensive (GC-allocated).
+	 * Performance: copying isn't ideal, but it's not visible in profiles. */
+	memcpy(&kr_layer_t_static, ctx, sizeof(*ctx));
+	const int ret = l_ffi_call_mod(L, 1);
 	/* The return codes are mixed at this point.  We need to return KR_STATE_* */
 	return ret < 0 ? KR_STATE_FAIL : ret;
 }
diff --git a/daemon/ffimodule.h b/daemon/ffimodule.h
index 564fa991b..81f5425d6 100644
--- a/daemon/ffimodule.h
+++ b/daemon/ffimodule.h
@@ -16,6 +16,12 @@
 
 #pragma once
 
+#include "lib/defines.h"
+#include "lib/layer.h"
+#include <lua.h>
+struct engine;
+struct kr_module;
+
 /**
  * Register Lua module as a FFI module.
  * This fabricates a standard module interface,
@@ -35,3 +41,8 @@ int ffimodule_register_lua(struct engine *engine, struct kr_module *module, cons
 int ffimodule_init(lua_State *L);
 void ffimodule_deinit(lua_State *L);
 
+/** Static storage for faster passing of layer function parameters to lua callbacks.
+ *
+ * We don't need to declare it in a header, but let's give it visibility. */
+KR_EXPORT kr_layer_t kr_layer_t_static;
+
diff --git a/daemon/lua/kres-gen.lua b/daemon/lua/kres-gen.lua
index ed48d753e..e59294bb7 100644
--- a/daemon/lua/kres-gen.lua
+++ b/daemon/lua/kres-gen.lua
@@ -251,7 +251,7 @@ struct kr_module {
 	void *lib;
 	void *data;
 };
-
+kr_layer_t kr_layer_t_static;
 typedef int32_t (*kr_stale_cb)(int32_t ttl, const knot_dname_t *owner, uint16_t type,
 				const struct kr_query *qry);
 
diff --git a/daemon/lua/kres-gen.sh b/daemon/lua/kres-gen.sh
index fd16e492c..c56ced706 100755
--- a/daemon/lua/kres-gen.sh
+++ b/daemon/lua/kres-gen.sh
@@ -124,6 +124,9 @@ ${CDEFS} ${LIBKRES} types <<-EOF
 	struct kr_module
 EOF
 
+# a static variable; the line might not be simple to generate
+printf "kr_layer_t kr_layer_t_static;"
+
 printf "
 typedef int32_t (*kr_stale_cb)(int32_t ttl, const knot_dname_t *owner, uint16_t type,
 				const struct kr_query *qry);
diff --git a/daemon/lua/sandbox.lua.in b/daemon/lua/sandbox.lua.in
index b3b939472..d31fcf02c 100644
--- a/daemon/lua/sandbox.lua.in
+++ b/daemon/lua/sandbox.lua.in
@@ -262,18 +262,17 @@ function modules_create_table_for_c(kr_module_ud)
 	})
 end
 
+local layer_ctx = ffi.C.kr_layer_t_static
 -- Utilities internal for lua layer glue; see ../ffimodule.c
-modules_ffi_layer_wrap1 = function (layer_cb, ctx_udata)
-	local ctx = ffi.cast('kr_layer_t **', ctx_udata)[0]
-	return layer_cb(ctx.state, ctx.req)
+modules_ffi_layer_wrap1 = function (layer_cb)
+	return layer_cb(layer_ctx.state, layer_ctx.req)
 end
-modules_ffi_layer_wrap2 = function (layer_cb, ctx_udata)
-	local ctx = ffi.cast('kr_layer_t **', ctx_udata)[0]
-	return layer_cb(ctx.state, ctx.req, ctx.pkt)
+modules_ffi_layer_wrap2 = function (layer_cb)
+	return layer_cb(layer_ctx.state, layer_ctx.req, layer_ctx.pkt)
 end
-modules_ffi_layer_wrap_checkout = function (layer_cb, ctx_udata)
-	local ctx = ffi.cast('kr_layer_t **', ctx_udata)[0]
-	return layer_cb(ctx.state, ctx.req, ctx.pkt, ctx.dst, ctx.is_stream)
+modules_ffi_layer_wrap_checkout = function (layer_cb)
+	return layer_cb(layer_ctx.state, layer_ctx.req, layer_ctx.pkt,
+					layer_ctx.dst, layer_ctx.is_stream)
 end
 modules_ffi_wrap_modcb = function (cb, kr_module_ud) -- this one isn't for layer
 	local kr_module = ffi.cast('struct kr_module **', kr_module_ud)[0]