svn commit: r324869 - in head/sys: cddl/dev/sdt kern sys

[Mateusz Guzik]

Author: mjg
Date: Sun Oct 22 20:22:23 2017
New Revision: 324869
URL: https://svnweb.freebsd.org/changeset/base/324869

Log:
  sdt: make all sdt probe sites test one variable
  
  This saves on cache misses at the expense of a slight grow of .text.
  
  Note this is a bandaid for lack of hotpatching.
  
  Discussed with:	markj

Modified:
  head/sys/cddl/dev/sdt/sdt.c
  head/sys/kern/kern_sdt.c
  head/sys/sys/sdt.h

Modified: head/sys/cddl/dev/sdt/sdt.c
==============================================================================
--- head/sys/cddl/dev/sdt/sdt.c	Sun Oct 22 20:22:11 2017	(r324868)
+++ head/sys/cddl/dev/sdt/sdt.c	Sun Oct 22 20:22:23 2017	(r324869)
@@ -76,6 +76,8 @@ static void	sdt_kld_unload_try(void *, struct linker_f
 
 static MALLOC_DEFINE(M_SDT, "SDT", "DTrace SDT providers");
 
+static int sdt_probes_enabled_count;
+
 static dtrace_pattr_t sdt_attr = {
 { DTRACE_STABILITY_EVOLVING, DTRACE_STABILITY_EVOLVING, DTRACE_CLASS_COMMON },
 { DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
@@ -208,6 +210,9 @@ sdt_enable(void *arg __unused, dtrace_id_t id, void *p
 	probe->sdtp_lf->nenabled++;
 	if (strcmp(probe->prov->name, "lockstat") == 0)
 		lockstat_enabled++;
+	sdt_probes_enabled_count++;
+	if (sdt_probes_enabled_count == 1)
+		sdt_probes_enabled = true;
 }
 
 static void
@@ -217,6 +222,9 @@ sdt_disable(void *arg __unused, dtrace_id_t id, void *
 
 	KASSERT(probe->sdtp_lf->nenabled > 0, ("no probes enabled"));
 
+	sdt_probes_enabled_count--;
+	if (sdt_probes_enabled_count == 0)
+		sdt_probes_enabled = false;
 	if (strcmp(probe->prov->name, "lockstat") == 0)
 		lockstat_enabled--;
 	probe->id = 0;

Modified: head/sys/kern/kern_sdt.c
==============================================================================
--- head/sys/kern/kern_sdt.c	Sun Oct 22 20:22:11 2017	(r324868)
+++ head/sys/kern/kern_sdt.c	Sun Oct 22 20:22:23 2017	(r324869)
@@ -37,6 +37,7 @@ SDT_PROVIDER_DEFINE(sdt);
  * dtrace_probe() when it loads.
  */
 sdt_probe_func_t sdt_probe_func = sdt_probe_stub;
+volatile bool __read_frequently sdt_probes_enabled;
 
 /*
  * This is a stub for probe calls in case kernel DTrace support isn't

Modified: head/sys/sys/sdt.h
==============================================================================
--- head/sys/sys/sdt.h	Sun Oct 22 20:22:11 2017	(r324868)
+++ head/sys/sys/sdt.h	Sun Oct 22 20:22:23 2017	(r324869)
@@ -80,6 +80,8 @@
 #include <sys/cdefs.h>
 #include <sys/linker_set.h>
 
+extern volatile bool sdt_probes_enabled;
+
 #ifndef KDTRACE_HOOKS
 
 #define SDT_PROVIDER_DEFINE(prov)
@@ -161,10 +163,12 @@ SET_DECLARE(sdt_argtypes_set, struct sdt_argtype);
 	extern struct sdt_probe sdt_##prov##_##mod##_##func##_##name[1]
 
 #define SDT_PROBE(prov, mod, func, name, arg0, arg1, arg2, arg3, arg4)	do {	\
-	if (__predict_false(sdt_##prov##_##mod##_##func##_##name->id))		\
+	if (__predict_false(sdt_probes_enabled)) {				\
+		if (__predict_false(sdt_##prov##_##mod##_##func##_##name->id))	\
 		(*sdt_probe_func)(sdt_##prov##_##mod##_##func##_##name->id,	\
 		    (uintptr_t) arg0, (uintptr_t) arg1, (uintptr_t) arg2,	\
 		    (uintptr_t) arg3, (uintptr_t) arg4);			\
+	} \
 } while (0)
 
 #define SDT_PROBE_ARGTYPE(prov, mod, func, name, num, type, xtype)		\