player/lua/defaults: add LuaJIT profiling support

gives us a way to properly profile the lua scripts to get some
verifiable way to test which "optimizations" work and which
don't.

currently only supports LuaJIT but the cli option is generically
named in case support for profiling other scripts is added in
the future.

Author: N-R-K

DOCS/man/options.rst

@@ -833,6 +833,12 @@ Program Behavior
     and overwrites the internal list with it. The latter is a key/value list
     option. See `List Options`_ for details.
 
+``--profile-script=<name[=path]>``, ``--profile-scripts=name1[=path1],name2[=path2],...``
+    Profile the given script(s) and dump a report to ``path`` when the script
+    exits. If no ``path`` is given, writes to standard out.
+
+    Currently only supports profiling lua scripts with LuaJIT.
+
 ``--merge-files``
     Pretend that all files passed to mpv are concatenated into a single, big
     file. This uses timeline/EDL support internally.

options/options.c

@@ -562,6 +562,8 @@ static const m_option_t mp_opts[] = {
     {"js-memory-report", OPT_BOOL(js_memory_report)},
 #endif
 #if HAVE_LUA
+    {"profile-scripts", OPT_STRINGLIST(profile_scripts)},
+    {"profile-script", OPT_CLI_ALIAS("profile-scripts-append")},
     {"osc", OPT_BOOL(lua_load_osc), .flags = UPDATE_BUILTIN_SCRIPTS},
     {"ytdl", OPT_BOOL(lua_load_ytdl), .flags = UPDATE_BUILTIN_SCRIPTS},
     {"ytdl-format", OPT_STRING(lua_ytdl_format)},

options/options.h

@@ -180,6 +180,7 @@ typedef struct MPOpts {
     char **reset_options;
     char **script_files;
     char **script_opts;
+    char **profile_scripts;
     bool js_memory_report;
     bool lua_load_osc;
     bool lua_load_ytdl;

player/lua/defaults.lua

@@ -25,6 +25,119 @@ function mp.get_opt(key, def)
     return val
 end
 
+local script_profile = nil
+
+local function get_profile_path()
+    local scripts = mp.get_property_native("options/profile-scripts", {}) or {}
+    for i = #scripts, 1, -1 do
+        local entry = scripts[i]
+        local name, path = entry:match("^([^=]+)=(.*)$")
+        if not name then
+            name = entry
+        end
+        if name == mp.script_name then
+            return path or ""
+        end
+    end
+    return nil
+end
+
+local function format_script_profile(state)
+    local entries = {}
+    for stack, samples in pairs(state.entries) do
+        entries[#entries + 1] = {stack = stack, samples = samples}
+    end
+
+    table.sort(entries, function(a, b)
+        if a.samples ~= b.samples then
+            return a.samples > b.samples
+        end
+        return a.stack < b.stack
+    end)
+
+    local lines = {
+        "script: " .. mp.script_name,
+        "samples: " .. state.total_samples,
+        "",
+    }
+
+    for _, entry in ipairs(entries) do
+        local percent = entry.samples * 100 / (state.total_samples or 1)
+        lines[#lines + 1] = string.format("%8d %6.2f%% %s",
+            entry.samples, percent, entry.stack)
+    end
+
+    return table.concat(lines, "\n")
+end
+
+local function write_script_profile(outpath, data)
+    local ok, err = true, ""
+    local out
+    local need_close = false
+
+    if outpath == "" then
+        out = io.stdout
+        outpath = "stdout"
+    else
+        out, err = io.open(outpath, "wb")
+        ok = out ~= nil
+        need_close = out ~= nil
+    end
+    if ok then
+        ok, err = out:write(data, "\n")
+    end
+    if ok then
+        ok, err = out:flush()
+    end
+    if need_close then
+        out:close()
+    end
+    if ok then
+        mp.log("info", "Profile data written to " .. outpath)
+    else
+        mp.log("error", "Could not write profile data to " ..
+            outpath .. ": " .. tostring(err))
+    end
+end
+
+local function stop_script_profile()
+    if not script_profile then
+        return
+    end
+
+    script_profile.profiler.stop()
+
+    local data = format_script_profile(script_profile)
+    write_script_profile(script_profile.output_path, data)
+    script_profile = nil
+end
+
+local function setup_script_profile()
+    local output_path = get_profile_path()
+    if not output_path then
+        return
+    end
+
+    local ok, profiler = pcall(require, "jit.profile")
+    if not ok then
+        error("Lua profiling requires LuaJIT")
+    end
+
+    script_profile = {
+        profiler = profiler,
+        total_samples = 0,
+        entries = {},
+        output_path = output_path,
+    }
+
+    profiler.start("fi4", function(thread, samples)
+        local stack = profiler.dumpstack(thread, "fZ;", -100)
+        script_profile.entries[stack] =
+            (script_profile.entries[stack] or 0) + samples
+        script_profile.total_samples = script_profile.total_samples + samples
+    end)
+end
+
 function mp.input_define_section(section, contents, flags)
     if flags == nil or flags == "" then
         flags = "default"
@@ -502,8 +615,11 @@ _G.print = mp.msg.info
 package.loaded["mp"] = mp
 package.loaded["mp.msg"] = mp.msg
 
+setup_script_profile()
+
 _G.mp_event_loop = function()
     mp.dispatch_events(true)
+    stop_script_profile()
 end
 
 local function call_event_handlers(e)