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Date:      Mon, 18 Feb 2019 14:21:41 +0000 (UTC)
From:      Vincenzo Maffione <vmaffione@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r344253 - head/sys/dev/netmap
Message-ID:  <201902181421.x1IELfEP027285@repo.freebsd.org>
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Author: vmaffione
Date: Mon Feb 18 14:21:41 2019
New Revision: 344253
URL: https://svnweb.freebsd.org/changeset/base/344253

Log:
  netmap: don't schedule kqueue notify task when kqueue is not used
  
  This change adds a counter (kqueue_users) to keep track of how many
  kqueue users are referencing a given struct nm_selinfo.
  In this way, nm_os_selwakeup() can schedule the kevent notification
  task only when kqueue is actually being used.
  This is important to avoid wasting CPU in the common case where
  kqueue is not used.
  
  Reviewed by:	Aleksandr Fedorov <aleksandr.fedorov@itglobal.com>
  MFC after:	1 week
  Differential Revision:	https://reviews.freebsd.org/D19177

Modified:
  head/sys/dev/netmap/netmap_freebsd.c
  head/sys/dev/netmap/netmap_kern.h

Modified: head/sys/dev/netmap/netmap_freebsd.c
==============================================================================
--- head/sys/dev/netmap/netmap_freebsd.c	Mon Feb 18 13:14:53 2019	(r344252)
+++ head/sys/dev/netmap/netmap_freebsd.c	Mon Feb 18 14:21:41 2019	(r344253)
@@ -105,6 +105,7 @@ int nm_os_selinfo_init(NM_SELINFO_T *si, const char *n
 	snprintf(si->mtxname, sizeof(si->mtxname), "nmkl%s", name);
 	mtx_init(&si->m, si->mtxname, NULL, MTX_DEF);
 	knlist_init_mtx(&si->si.si_note, &si->m);
+	si->kqueue_users = 0;
 
 	return (0);
 }
@@ -1351,7 +1352,9 @@ void
 nm_os_selwakeup(struct nm_selinfo *si)
 {
 	selwakeuppri(&si->si, PI_NET);
-	taskqueue_enqueue(si->ntfytq, &si->ntfytask);
+	if (si->kqueue_users > 0) {
+		taskqueue_enqueue(si->ntfytq, &si->ntfytask);
+	}
 }
 
 void
@@ -1364,20 +1367,28 @@ static void
 netmap_knrdetach(struct knote *kn)
 {
 	struct netmap_priv_d *priv = (struct netmap_priv_d *)kn->kn_hook;
-	struct selinfo *si = &priv->np_si[NR_RX]->si;
+	struct nm_selinfo *si = priv->np_si[NR_RX];
 
-	nm_prinf("remove selinfo %p", si);
-	knlist_remove(&si->si_note, kn, /*islocked=*/0);
+	knlist_remove(&si->si.si_note, kn, /*islocked=*/0);
+	NMG_LOCK();
+	KASSERT(si->kqueue_users > 0, ("kqueue_user underflow on %s",
+	    si->mtxname));
+	si->kqueue_users--;
+	nm_prinf("kqueue users for %s: %d", si->mtxname, si->kqueue_users);
+	NMG_UNLOCK();
 }
 
 static void
 netmap_knwdetach(struct knote *kn)
 {
 	struct netmap_priv_d *priv = (struct netmap_priv_d *)kn->kn_hook;
-	struct selinfo *si = &priv->np_si[NR_TX]->si;
+	struct nm_selinfo *si = priv->np_si[NR_TX];
 
-	nm_prinf("remove selinfo %p", si);
-	knlist_remove(&si->si_note, kn, /*islocked=*/0);
+	knlist_remove(&si->si.si_note, kn, /*islocked=*/0);
+	NMG_LOCK();
+	si->kqueue_users--;
+	nm_prinf("kqueue users for %s: %d", si->mtxname, si->kqueue_users);
+	NMG_UNLOCK();
 }
 
 /*
@@ -1465,6 +1476,10 @@ netmap_kqfilter(struct cdev *dev, struct knote *kn)
 	kn->kn_fop = (ev == EVFILT_WRITE) ?
 		&netmap_wfiltops : &netmap_rfiltops;
 	kn->kn_hook = priv;
+	NMG_LOCK();
+	si->kqueue_users++;
+	nm_prinf("kqueue users for %s: %d", si->mtxname, si->kqueue_users);
+	NMG_UNLOCK();
 	knlist_add(&si->si.si_note, kn, /*islocked=*/0);
 
 	return 0;

Modified: head/sys/dev/netmap/netmap_kern.h
==============================================================================
--- head/sys/dev/netmap/netmap_kern.h	Mon Feb 18 13:14:53 2019	(r344252)
+++ head/sys/dev/netmap/netmap_kern.h	Mon Feb 18 14:21:41 2019	(r344253)
@@ -132,11 +132,14 @@ struct netmap_adapter *netmap_getna(if_t ifp);
 #define MBUF_QUEUED(m)		1
 
 struct nm_selinfo {
+	/* Support for select(2) and poll(2). */
 	struct selinfo si;
+	/* Support for kqueue(9). See comments in netmap_freebsd.c */
 	struct taskqueue *ntfytq;
 	struct task ntfytask;
 	struct mtx m;
 	char mtxname[32];
+	int kqueue_users;
 };

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