prof_state_toggle: keep a count of CPUs with profiling enabled

On MULTIPROCESSOR systems, the following sequence of kgmon(8)
invocations leaves the statclock() frequency at stathz when there is
still a CPU on the system where the gmon state is GMON_PROF_ON:

	# kgmon -c 0 -b
	# kgmon -c 1 -b
	# kgmon -c 0 -h

The problem is that we aren't counting CPUs with profiling enabled.
Add "gmon_cpu_count" to keep a count.  Call startprofclock() for the
first CPU to enable profiling and stopprofclock() for the last CPU to
disable profiling.

diff --git a/sys/kern/subr_prof.c b/sys/kern/subr_prof.c
index 5f944cf..c578c93 100644 (file)
--- a/sys/kern/subr_prof.c
+++ b/sys/kern/subr_prof.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: subr_prof.c,v 1.32 2023/04/25 00:58:47 cheloha Exp $  */
+/*     $OpenBSD: subr_prof.c,v 1.33 2023/04/25 01:32:36 cheloha Exp $  */
 /*     $NetBSD: subr_prof.c,v 1.12 1996/04/22 01:38:50 christos Exp $  */
 
 /*-
@@ -55,6 +55,7 @@
  * until we're sure they are in a sane state.
  */
 int gmoninit = 0;
+u_int gmon_cpu_count;          /* [K] number of CPUs with profiling enabled */
 
 extern char etext[];
 
@@ -126,6 +127,8 @@ prof_state_toggle(struct gmonparam *gp, int oldstate)
 {
        int error = 0;
 
+       KERNEL_ASSERT_LOCKED();
+
        if (gp->state == oldstate)
                return (0);
 
@@ -138,15 +141,18 @@ prof_state_toggle(struct gmonparam *gp, int oldstate)
                 */
                error = db_prof_enable();
 #endif
-               if (error == 0)
-                       startprofclock(&process0);
+               if (error == 0) {
+                       if (++gmon_cpu_count == 1)
+                               startprofclock(&process0);
+               }
                break;
        default:
                error = EINVAL;
                gp->state = GMON_PROF_OFF;
                /* FALLTHROUGH */
        case GMON_PROF_OFF:
-               stopprofclock(&process0);
+               if (--gmon_cpu_count == 0)
+                       stopprofclock(&process0);
 #if !defined(GPROF)
                db_prof_disable();
 #endif