MINOR: startup: tune.renice.{startup,runtime} allow to change priorities

This commit introduces the tune.renice.startup and tune.renice.runtime
global keywords that allows to change the priority with setpriority().

tune.renice.startup is parsed and applied during the discovery mode so
the nice value is applied on the master process or the standalone
process for configuration parsing. If this keyword is used alone, the
value is inherited by any process forked from the master.

tune.renice.runtime is applied after configuration parsing, so in the
worker or a standalone process. Combined with tune.renice.startup it
allows to have a different nice value during configuration parsing and
during runtime.

The feature was discussed in github issue #1919.

Example:

   global
        tune.renice.startup 15
        tune.renice.runtime 0

doc/configuration.txt

@@ -1524,6 +1524,8 @@ The following keywords are supported in the "global" section :
    - tune.quic.retry-threshold
    - tune.quic.socket-owner
    - tune.quic.zero-copy-fwd-send
+   - tune.renice.runtime
+   - tune.renice.startup
    - tune.rcvbuf.backend
    - tune.rcvbuf.client
    - tune.rcvbuf.frontend
@@ -4060,6 +4062,24 @@ tune.quic.zero-copy-fwd-send { on | off }
 
   See also: tune.disable-zero-copy-forwarding
 
+tune.renice.runtime <number>
+  This configuration option takes a value between -20 and 19. It applies a
+  scheduling priority as documented in man 2 setpriority. This priority is
+  applied after the configuration parsing, which means only the worker or the
+  standalone process will apply it. It is usually configured to set a higher
+  priority than a process doing configuration parsing (tune.renice.startup).
+
+  See also: tune.renice.startup
+
+tune.renice.startup <number>
+  This configuration option takes a value between -20 and 19. It applies a
+  scheduling priority as documented in man 2 setpriority. This priority is
+  applied before applying the rest of the configuration which can be useful if
+  you want to lower the priority for configuration parsing. In master-worker
+  mode, this priority is kept by the master after configuration parsing.
+
+  See also: tune.renice.runtime
+
 tune.rcvbuf.backend <number>
 tune.rcvbuf.frontend <number>
   For the kernel socket receive buffer size on non-connected sockets to this

include/haproxy/global-t.h

@@ -190,6 +190,8 @@ struct global {
 		int pool_low_count;   /* max number of opened fd before we stop using new idle connections */
 		int pool_high_count;  /* max number of opened fd before we start killing idle connections when creating new connections */
 		size_t pool_cache_size;    /* per-thread cache size per pool (defaults to CONFIG_HAP_POOL_CACHE_SIZE) */
+		int renice_startup;     /* startup nice()+100 value during startup; 0 = unset */
+		int renice_runtime;     /* startup nice()+100 value during runtime; 0 = unset */
 		unsigned short idle_timer; /* how long before an empty buffer is considered idle (ms) */
 		unsigned short no_zero_copy_fwd; /* Flags to disable zero-copy fast-forwarding (global & per-protocols) */
 		int nb_stk_ctr;       /* number of stick counters, defaults to MAX_SESS_STKCTR */

src/cfgparse-global.c

@@ -8,6 +8,7 @@
 #include <grp.h>
 #include <errno.h>
 #include <sys/types.h>
+#include <sys/resource.h>
 #include <sys/stat.h>
 #include <unistd.h>
 
@@ -1540,6 +1541,55 @@ static int cfg_parse_global_parser_pause(char **args, int section_type,
 	return 0;
 }
 
+/* config parser for global "tune.renice.startup" and "tune.renice.runtime",
+ * accepts -20 to +19 inclusive, stored as 80..119.
+ */
+static int cfg_parse_tune_renice(char **args, int section_type, struct proxy *curpx,
+                                const struct proxy *defpx, const char *file, int line,
+                                char **err)
+{
+	int prio;
+	char *stop;
+
+	if (too_many_args(1, args, err, NULL))
+		return -1;
+
+	prio = strtol(args[1], &stop, 10);
+	if ((*stop != '\0') || (prio < -20 || prio > 19)) {
+		memprintf(err, "'%s' only supports values between -20 and 19 inclusive (was given %d)", args[0], prio);
+		return -1;
+	}
+
+	/* 'runtime' vs 'startup' */
+	if (args[0][12] == 'r') {
+		global.tune.renice_runtime = prio + 100;
+	} else if (args[0][12] == 's') {
+		/* 'startup' executes only in discovery mode */
+
+		global.tune.renice_startup = prio + 100;
+		if (setpriority(PRIO_PROCESS, 0, prio) == -1)
+			ha_warning("couldn't set the runtime nice value to %d: %s\n", prio, strerror(errno));
+	} else {
+		BUG_ON(1, "Triggered in cfg_parse_tune_renice() by unsupported keyword.\n");
+	}
+
+	return 0;
+}
+/* config parser for global "tune.renice.startup" and "tune.renice.runtime",
+ * accepts -20 to +19 inclusive, stored as 80..119.
+ */
+static int cfg_parse_tune_renice_startup(char **args, int section_type, struct proxy *curpx,
+                                         const struct proxy *defpx, const char *file, int line,
+                                         char **err)
+{
+	/* 'startup' executes only in discovery mode */
+	if (!(global.mode & MODE_DISCOVERY))
+		return 0;
+
+	return cfg_parse_tune_renice(args, section_type, curpx, defpx, file, line, err);
+}
+
+
 static struct cfg_kw_list cfg_kws = {ILH, {
 	{ CFG_GLOBAL, "prealloc-fd", cfg_parse_prealloc_fd },
 	{ CFG_GLOBAL, "force-cfg-parser-pause", cfg_parse_global_parser_pause, KWF_EXPERIMENTAL },
@@ -1563,6 +1613,8 @@ static struct cfg_kw_list cfg_kws = {ILH, {
 	{ CFG_GLOBAL, "tune.bufsize", cfg_parse_global_tune_opts },
 	{ CFG_GLOBAL, "tune.maxrewrite", cfg_parse_global_tune_opts },
 	{ CFG_GLOBAL, "tune.idletimer", cfg_parse_global_tune_opts },
+	{ CFG_GLOBAL, "tune.renice.startup", cfg_parse_tune_renice_startup, KWF_DISCOVERY },
+	{ CFG_GLOBAL, "tune.renice.runtime", cfg_parse_tune_renice, 0 },
 	{ CFG_GLOBAL, "tune.rcvbuf.client", cfg_parse_global_tune_opts },
 	{ CFG_GLOBAL, "tune.rcvbuf.server", cfg_parse_global_tune_opts },
 	{ CFG_GLOBAL, "tune.sndbuf.client", cfg_parse_global_tune_opts },

src/haproxy.c

@@ -3942,6 +3942,15 @@ int main(int argc, char **argv)
 		}
 	}
 
+        /* applies the renice value in the worker or standalone after configuration parsing
+         * but before chaning identity */
+        if (!master && global.tune.renice_runtime) {
+		if (setpriority(PRIO_PROCESS, 0, global.tune.renice_runtime - 100) == -1) {
+			ha_warning("[%s.main()] couldn't set the runtime nice value to %d: %s\n",
+			           argv[0], global.tune.renice_runtime - 100, strerror(errno));
+		}
+	}
+
 	/* Must chroot and setgid/setuid in the children */
 	/* chroot if needed */
 	if (global.chroot != NULL) {