From 5da38b3b08a4c55a8ecc7f2139501ae35470a6f1 Mon Sep 17 00:00:00 2001
From: kib <kib@FreeBSD.org>
Date: Sun, 25 Dec 2016 19:49:35 +0000
Subject: [PATCH] Some optimizations for kqueue timers.

There is no need to do two allocations per kqueue timer. Gather all
data needed by the timer callout into the structure and allocate it at
once.

Use the structure to preserve the result of timer2sbintime(), to not
perform repeated 64bit calculations in callout.

Remove tautological casts.
Remove now unused p_nexttime [1].

Noted by:	markj [1]
Reviewed by:	markj (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
X-MFC note:	do not remove p_nexttime
Differential revision:	https://reviews.freebsd.org/D8901
---
 sys/kern/kern_event.c | 52 +++++++++++++++++++++++--------------------
 sys/sys/event.h       |  1 -
 2 files changed, 28 insertions(+), 25 deletions(-)

diff --git a/sys/kern/kern_event.c b/sys/kern/kern_event.c
index f30b56b169d5..957853623051 100644
--- a/sys/kern/kern_event.c
+++ b/sys/kern/kern_event.c
@@ -631,23 +631,29 @@ timer2sbintime(intptr_t data, int flags)
 	return (-1);
 }
 
+struct kq_timer_cb_data {
+	struct callout c;
+	sbintime_t next;	/* next timer event fires at */
+	sbintime_t to;		/* precalculated timer period */
+};
+
 static void
 filt_timerexpire(void *knx)
 {
-	struct callout *calloutp;
 	struct knote *kn;
+	struct kq_timer_cb_data *kc;
 
 	kn = knx;
 	kn->kn_data++;
 	KNOTE_ACTIVATE(kn, 0);	/* XXX - handle locking */
 
-	if ((kn->kn_flags & EV_ONESHOT) != EV_ONESHOT) {
-		calloutp = (struct callout *)kn->kn_hook;
-		*kn->kn_ptr.p_nexttime += timer2sbintime(kn->kn_sdata, 
-		    kn->kn_sfflags);
-		callout_reset_sbt_on(calloutp, *kn->kn_ptr.p_nexttime, 0,
-		    filt_timerexpire, kn, PCPU_GET(cpuid), C_ABSOLUTE);
-	}
+	if ((kn->kn_flags & EV_ONESHOT) != 0)
+		return;
+
+	kc = kn->kn_ptr.p_v;
+	kc->next += kc->to;
+	callout_reset_sbt_on(&kc->c, kc->next, 0, filt_timerexpire, kn,
+	    PCPU_GET(cpuid), C_ABSOLUTE);
 }
 
 /*
@@ -656,16 +662,16 @@ filt_timerexpire(void *knx)
 static int
 filt_timerattach(struct knote *kn)
 {
-	struct callout *calloutp;
+	struct kq_timer_cb_data *kc;
 	sbintime_t to;
 	unsigned int ncallouts;
 
-	if ((intptr_t)kn->kn_sdata < 0)
+	if (kn->kn_sdata < 0)
 		return (EINVAL);
-	if ((intptr_t)kn->kn_sdata == 0 && (kn->kn_flags & EV_ONESHOT) == 0)
+	if (kn->kn_sdata == 0 && (kn->kn_flags & EV_ONESHOT) == 0)
 		kn->kn_sdata = 1;
 	/* Only precision unit are supported in flags so far */
-	if (kn->kn_sfflags & ~NOTE_TIMER_PRECMASK)
+	if ((kn->kn_sfflags & ~NOTE_TIMER_PRECMASK) != 0)
 		return (EINVAL);
 
 	to = timer2sbintime(kn->kn_sdata, kn->kn_sfflags);
@@ -680,13 +686,12 @@ filt_timerattach(struct knote *kn)
 
 	kn->kn_flags |= EV_CLEAR;		/* automatically set */
 	kn->kn_status &= ~KN_DETACHED;		/* knlist_add clears it */
-	kn->kn_ptr.p_nexttime = malloc(sizeof(sbintime_t), M_KQUEUE, M_WAITOK);
-	calloutp = malloc(sizeof(*calloutp), M_KQUEUE, M_WAITOK);
-	callout_init(calloutp, 1);
-	kn->kn_hook = calloutp;
-	*kn->kn_ptr.p_nexttime = to + sbinuptime();
-	callout_reset_sbt_on(calloutp, *kn->kn_ptr.p_nexttime, 0,
-	    filt_timerexpire, kn, PCPU_GET(cpuid), C_ABSOLUTE);
+	kn->kn_ptr.p_v = kc = malloc(sizeof(*kc), M_KQUEUE, M_WAITOK);
+	callout_init(&kc->c, 1);
+	kc->next = to + sbinuptime();
+	kc->to = to;
+	callout_reset_sbt_on(&kc->c, kc->next, 0, filt_timerexpire, kn,
+	    PCPU_GET(cpuid), C_ABSOLUTE);
 
 	return (0);
 }
@@ -694,13 +699,12 @@ filt_timerattach(struct knote *kn)
 static void
 filt_timerdetach(struct knote *kn)
 {
-	struct callout *calloutp;
+	struct kq_timer_cb_data *kc;
 	unsigned int old;
 
-	calloutp = (struct callout *)kn->kn_hook;
-	callout_drain(calloutp);
-	free(calloutp, M_KQUEUE);
-	free(kn->kn_ptr.p_nexttime, M_KQUEUE);
+	kc = kn->kn_ptr.p_v;
+	callout_drain(&kc->c);
+	free(kc, M_KQUEUE);
 	old = atomic_fetchadd_int(&kq_ncallouts, -1);
 	KASSERT(old > 0, ("Number of callouts cannot become negative"));
 	kn->kn_status |= KN_DETACHED;	/* knlist_remove sets it */
diff --git a/sys/sys/event.h b/sys/sys/event.h
index 139caff46c1a..dc0046998d40 100644
--- a/sys/sys/event.h
+++ b/sys/sys/event.h
@@ -231,7 +231,6 @@ struct knote {
 		struct		proc *p_proc;	/* proc pointer */
 		struct		kaiocb *p_aio;	/* AIO job pointer */
 		struct		aioliojob *p_lio;	/* LIO job pointer */
-		sbintime_t	*p_nexttime;	/* next timer event fires at */
 		void		*p_v;		/* generic other pointer */
 	} kn_ptr;
 	struct			filterops *kn_fop;