Fix kernel profiling on MP systems by using per-CPU buffer. Previously

various CPUs were iterating over the same global buffer at the same
time to modify it and never ended.

This diff includes some ideas submited by Thor Simon to NetBSD via miod@.

ok mikeb@, haesbaert@

1 files changed, 76 insertions, 32 deletions

diff --git a/sys/kern/subr_prof.c b/sys/kern/subr_prof.c
index 04e5003b1f6..a7eff46dc2f 100644
--- a/sys/kern/subr_prof.c
+++ b/sys/kern/subr_prof.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: subr_prof.c,v 1.21 2012/08/02 03:18:48 guenther Exp $	*/
+/*	$OpenBSD: subr_prof.c,v 1.22 2013/02/11 17:05:25 mpi Exp $	*/
 /*	$NetBSD: subr_prof.c,v 1.12 1996/04/22 01:38:50 christos Exp $	*/
 
 /*-
@@ -49,49 +49,75 @@
 #include <uvm/uvm_extern.h>
 
 /*
- * Froms is actually a bunch of unsigned shorts indexing tos
+ * Protect CPUs from executing profiling while they are not yet in a
+ * sane state.
  */
-struct gmonparam _gmonparam = { GMON_PROF_OFF };
+int gmoninit = 0;
 
 extern char etext[];
 
+#define ROUNDDOWN(x,y)	(((x)/(y))*(y))
+#define ROUNDUP(x,y)	((((x)+(y)-1)/(y))*(y))
 
 void
 kmstartup(void)
 {
+	CPU_INFO_ITERATOR cii;
+	struct cpu_info *ci;
+	struct gmonparam *p;
+	u_long lowpc, highpc, textsize;
+	u_long kcountsize, fromssize, tossize;
+	long tolimit;
 	char *cp;
-	struct gmonparam *p = &_gmonparam;
 	int size;
 
 	/*
 	 * Round lowpc and highpc to multiples of the density we're using
 	 * so the rest of the scaling (here and in gprof) stays in ints.
 	 */
-	p->lowpc = ROUNDDOWN(KERNBASE, HISTFRACTION * sizeof(HISTCOUNTER));
-	p->highpc = ROUNDUP((u_long)etext, HISTFRACTION * sizeof(HISTCOUNTER));
-	p->textsize = p->highpc - p->lowpc;
+	lowpc = ROUNDDOWN(KERNBASE, HISTFRACTION * sizeof(HISTCOUNTER));
+	highpc = ROUNDUP((u_long)etext, HISTFRACTION * sizeof(HISTCOUNTER));
+	textsize = highpc - lowpc;
 	printf("Profiling kernel, textsize=%ld [%lx..%lx]\n",
-	       p->textsize, p->lowpc, p->highpc);
-	p->kcountsize = p->textsize / HISTFRACTION;
-	p->hashfraction = HASHFRACTION;
-	p->fromssize = p->textsize / HASHFRACTION;
-	p->tolimit = p->textsize * ARCDENSITY / 100;
-	if (p->tolimit < MINARCS)
-		p->tolimit = MINARCS;
-	else if (p->tolimit > MAXARCS)
-		p->tolimit = MAXARCS;
-	p->tossize = p->tolimit * sizeof(struct tostruct);
-	size = p->kcountsize + p->fromssize + p->tossize;
-	cp = (char *)uvm_km_zalloc(kernel_map, round_page(size));
-	if (cp == 0) {
-		printf("No memory for profiling.\n");
-		return;
+	    textsize, lowpc, highpc);
+	kcountsize = textsize / HISTFRACTION;
+	fromssize = textsize / HASHFRACTION;
+	tolimit = textsize * ARCDENSITY / 100;
+	if (tolimit < MINARCS)
+		tolimit = MINARCS;
+	else if (tolimit > MAXARCS)
+		tolimit = MAXARCS;
+	tossize = tolimit * sizeof(struct tostruct);
+	size = sizeof(*p) + kcountsize + fromssize + tossize;
+
+	/* Allocate and initialize one profiling buffer per CPU. */
+	CPU_INFO_FOREACH(cii, ci) {
+		cp = km_alloc(round_page(size), &kv_any, &kp_zero, &kd_nowait);
+		if (cp == NULL) {
+			printf("No memory for profiling.\n");
+			return;
+		}
+
+		p = (struct gmonparam *)cp;
+		cp += sizeof(*p);
+		p->tos = (struct tostruct *)cp;
+		cp += tossize;
+		p->kcount = (u_short *)cp;
+		cp += kcountsize;
+		p->froms = (u_short *)cp;
+
+		p->state = GMON_PROF_OFF;
+		p->lowpc = lowpc;
+		p->highpc = highpc;
+		p->textsize = textsize;
+		p->hashfraction = HASHFRACTION;
+		p->kcountsize = kcountsize;
+		p->fromssize = fromssize;
+		p->tolimit = tolimit;
+		p->tossize = tossize;
+
+		ci->ci_gmon = p;
 	}
-	p->tos = (struct tostruct *)cp;
-	cp += p->tossize;
-	p->kcount = (u_short *)cp;
-	cp += p->kcountsize;
-	p->froms = (u_short *)cp;
 }
 
 /*
@@ -101,14 +127,32 @@ int
 sysctl_doprof(int *name, u_int namelen, void *oldp, size_t *oldlenp, void *newp,
     size_t newlen)
 {
-	struct gmonparam *gp = &_gmonparam;
-	int error;
+	CPU_INFO_ITERATOR cii;
+	struct cpu_info *ci;
+	struct gmonparam *gp = NULL;
+	int error, cpuid, op;
 
-	/* all sysctl names at this level are terminal */
-	if (namelen != 1)
+	/* all sysctl names at this level are name and field */
+	if (namelen != 2)
 		return (ENOTDIR);		/* overloaded */
 
-	switch (name[0]) {
+	op = name[0];
+	cpuid = name[1];
+
+	CPU_INFO_FOREACH(cii, ci) {
+		if (cpuid == CPU_INFO_UNIT(ci)) {
+			gp = ci->ci_gmon;
+			break;
+		}
+	}
+
+	if (gp == NULL)
+		return (EOPNOTSUPP);
+
+	/* Assume that if we're here it is safe to execute profiling. */
+	gmoninit = 1;
+
+	switch (op) {
 	case GPROF_STATE:
 		error = sysctl_int(oldp, oldlenp, newp, newlen, &gp->state);
 		if (error)