From 314eeef29042a1bdbe1d9365eeba2649db63f662 Mon Sep 17 00:00:00 2001
From: Stanislav Sedov <stas@FreeBSD.org>
Date: Tue, 1 Dec 2015 00:24:54 +0000
Subject: [PATCH] Make the number of fasttrap probes and the size of the trace
 points hash table tunable via sysctl or kernel tunables.

Illumos allows this parameters to be changed via the fasttrap.conf configuration
file, but FreeBSD code hardcoded the parameters.  Expose them under
the kern.dtrace.fasttrap sysctl tree.

MFC after:	2 weeks
---
 .../opensolaris/uts/common/dtrace/fasttrap.c  | 29 ++++++++++++++-----
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c b/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
index df485670abdd..348222c79c16 100644
--- a/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/dtrace/fasttrap.c
@@ -63,6 +63,7 @@
 #ifndef illumos
 #include <sys/dtrace_bsd.h>
 #include <sys/eventhandler.h>
+#include <sys/sysctl.h>
 #include <sys/u8_textprep.h>
 #include <sys/user.h>
 #include <vm/vm.h>
@@ -172,13 +173,14 @@ static volatile uint64_t fasttrap_mod_gen;
 
 /*
  * When the fasttrap provider is loaded, fasttrap_max is set to either
- * FASTTRAP_MAX_DEFAULT or the value for fasttrap-max-probes in the
- * fasttrap.conf file. Each time a probe is created, fasttrap_total is
- * incremented by the number of tracepoints that may be associated with that
- * probe; fasttrap_total is capped at fasttrap_max.
+ * FASTTRAP_MAX_DEFAULT, or the value for fasttrap-max-probes in the
+ * fasttrap.conf file (Illumos), or the value provied in the loader.conf (FreeBSD).
+ * Each time a probe is created, fasttrap_total is incremented by the number
+ * of tracepoints that may be associated with that probe; fasttrap_total is capped
+ * at fasttrap_max.
  */
 #define	FASTTRAP_MAX_DEFAULT		250000
-static uint32_t fasttrap_max;
+static uint32_t fasttrap_max = FASTTRAP_MAX_DEFAULT;
 static uint32_t fasttrap_total;
 
 /*
@@ -226,6 +228,17 @@ static kmutex_t fasttrap_cpuc_pid_lock[MAXCPU];
 static eventhandler_tag fasttrap_thread_dtor_tag;
 #endif
 
+static unsigned long tpoints_hash_size = FASTTRAP_TPOINTS_DEFAULT_SIZE;
+
+#ifdef __FreeBSD__
+SYSCTL_DECL(_kern_dtrace);
+SYSCTL_NODE(_kern_dtrace, OID_AUTO, fasttrap, CTLFLAG_RD, 0, "DTrace fasttrap parameters");
+SYSCTL_UINT(_kern_dtrace_fasttrap, OID_AUTO, max_probes, CTLFLAG_RWTUN, &fasttrap_max,
+    FASTTRAP_MAX_DEFAULT, "Maximum number of fasttrap probes");
+SYSCTL_ULONG(_kern_dtrace_fasttrap, OID_AUTO, tpoints_hash_size, CTLFLAG_RDTUN, &tpoints_hash_size,
+    FASTTRAP_TPOINTS_DEFAULT_SIZE, "Size of the tracepoint hash table");
+#endif
+
 static int
 fasttrap_highbit(ulong_t i)
 {
@@ -2480,8 +2493,6 @@ fasttrap_load(void)
 #ifdef illumos
 	fasttrap_max = ddi_getprop(DDI_DEV_T_ANY, devi, DDI_PROP_DONTPASS,
 	    "fasttrap-max-probes", FASTTRAP_MAX_DEFAULT);
-#else
-	fasttrap_max = FASTTRAP_MAX_DEFAULT;
 #endif
 	fasttrap_total = 0;
 
@@ -2492,12 +2503,14 @@ fasttrap_load(void)
 	nent = ddi_getprop(DDI_DEV_T_ANY, devi, DDI_PROP_DONTPASS,
 	    "fasttrap-hash-size", FASTTRAP_TPOINTS_DEFAULT_SIZE);
 #else
-	nent = FASTTRAP_TPOINTS_DEFAULT_SIZE;
+	nent = tpoints_hash_size;
 #endif
 
 	if (nent == 0 || nent > 0x1000000)
 		nent = FASTTRAP_TPOINTS_DEFAULT_SIZE;
 
+	tpoints_hash_size = nent;
+
 	if (ISP2(nent))
 		fasttrap_tpoints.fth_nent = nent;
 	else