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Date: Tue, 19 Oct 2010 11:59:56 +0300
From: Jaakko Heinonen <jh@FreeBSD.org>
To: David Xu <davidxu@freebsd.org>
Message-ID: <20101019085955.GA4865@jh>
References: <4C961009.6080609@freebsd.org> <4C96ED40.7070206@DataIX.net>
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User-Agent: Mutt/1.5.21 (2010-09-15)
Cc: freebsd-current@freebsd.org
Subject: Re: sysctl -a is slow
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On 2010-09-20, David Xu wrote:
> I redirect all output to a disk file, and it still needs 1 second to
> complete, this machine is dual-core pentium E5500, faster than previous
> one which is a dual-core AMD 5000+ machine, the 5000+ needs 2
> seconds to complete.
> 
> $/usr/bin/time sysctl -b kern.geom.confdot > sysctl_geom_confdot.txt
>         1.00 real         0.00 user         0.00 sys

I couldn't reproduce the problem myself but I bet that it's a lost
wakeup in g_waitfor_event(). Can you try this patch?

%%%
Index: sys/geom/geom_event.c
===================================================================
--- sys/geom/geom_event.c	(revision 214048)
+++ sys/geom/geom_event.c	(working copy)
@@ -220,11 +220,12 @@ one_event(void)
 	mtx_lock(&g_eventlock);
 	TAILQ_REMOVE(&g_events, ep, events);
 	ep->flag &= ~EV_INPROGRESS;
-	mtx_unlock(&g_eventlock);
 	if (ep->flag & EV_WAKEUP) {
 		ep->flag |= EV_DONE;
 		wakeup(ep);
+		mtx_unlock(&g_eventlock);
 	} else {
+		mtx_unlock(&g_eventlock);
 		g_free(ep);
 	}
 	g_topology_unlock();
@@ -365,11 +366,14 @@ g_waitfor_event(g_event_t *func, void *a
 	va_end(ap);
 	if (error)
 		return (error);
-	do 
-		tsleep(ep, PRIBIO, "g_waitfor_event", hz);
-	while (!(ep->flag & EV_DONE));
+
+	mtx_lock(&g_eventlock);
+	while (!(ep->flag & EV_DONE))
+		msleep(ep, &g_eventlock, PRIBIO, "g_waitfor_event", hz);
 	if (ep->flag & EV_CANCELED)
 		error = EAGAIN;
+	mtx_unlock(&g_eventlock);
+
 	g_free(ep);
 	return (error);
 }
%%%

-- 
Jaakko