racct: Simplify skipping idle process in the throttling daemon

In racctd(), commit c72188d85a79 ("racct: Improve handling of the pcpu
resource") added a superfluous test to skip the idle process when
computing the resource usage and checking for limits, consisting of
a comparison of the considered process' pointer with that of the process of
the first CPU's idle thread.  The P_IDLEPROC flag introduced in commit
33be1632047c ("racct: Fix accounting of CPU time for the system idle
process") is sufficient and simpler for this purpose.

In the second loop throttling processes based on their %CPU usage, the
test excluding processes not in PRS_NORMAL was not consistent with that
of the first loop (which tests for the idle process also).  This had no
practical consequences except a superfluous call to
racct_pcpu_available() as the RACCT_PCTCPU counter stays at 0 on the
idle process (because of the first loop).  Factor out the test in the
new racct_proc_to_skip() function.

No functional change intended.

Reviewed by:    markj
MFC after:      3 days
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D53455

1 files changed, 9 insertions, 10 deletions

diff --git a/sys/kern/kern_racct.c b/sys/kern/kern_racct.c
index 2aab151aba08..17b64ad00bb5 100644
--- a/sys/kern/kern_racct.c
+++ b/sys/kern/kern_racct.c
@@ -1236,16 +1236,20 @@ racct_updatepcpu_containers(void)
 	    racct_updatepcpu_post, NULL, NULL);
 }
 
+static bool
+racct_proc_to_skip(const struct proc *p)
+{
+	PROC_LOCK_ASSERT(p, MA_OWNED);
+	return (p->p_state != PRS_NORMAL || (p->p_flag & P_IDLEPROC) != 0);
+}
+
 static void
 racctd(void)
 {
 	struct proc *p;
-	struct proc *idle;
 
 	ASSERT_RACCT_ENABLED();
 
-	idle = STAILQ_FIRST(&cpuhead)->pc_idlethread->td_proc;
-
 	for (;;) {
 		racct_decay();
 
@@ -1253,12 +1257,7 @@ racctd(void)
 
 		FOREACH_PROC_IN_SYSTEM(p) {
 			PROC_LOCK(p);
-			if (p == idle) {
-				PROC_UNLOCK(p);
-				continue;
-			}
-			if (p->p_state != PRS_NORMAL ||
-			    (p->p_flag & P_IDLEPROC) != 0) {
+			if (racct_proc_to_skip(p)) {
 				PROC_UNLOCK(p);
 				continue;
 			}
@@ -1284,7 +1283,7 @@ racctd(void)
 		 */
 		FOREACH_PROC_IN_SYSTEM(p) {
 			PROC_LOCK(p);
-			if (p->p_state != PRS_NORMAL) {
+			if (racct_proc_to_skip(p)) {
 				PROC_UNLOCK(p);
 				continue;
 			}