Consistently "high" CPU load on 10.0-STABLE
Jeremy Chadwick
jdc at koitsu.org
Sun Jul 20 17:35:26 UTC 2014
Yes and no, heh... :-)
Using top -a -H -S -z -s 1 and watching very very closely, what I end up
seeing is that occasionally syncer reaches WCPU percentages of around
0.50% (or maybe higher) -- but when that happens, the actual load average
**does not** suddenly increase.
The load just seems to go from like 0.01 or 0.02 to 0.12 or 0.20
sporadically with no real evidence of "why" in top. Possibly this is
because I'm using -s 1 (one second update intervals) and whatever
happens is so fast/quick that it lasts less than a second / top doesn't
catch it, but still impacts the load?
Anyway, the "top" processes per TIME in the above command are here:
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
17 root 16 - 0K 16K syncer 2 1:31 0.49% syncer
0 root -16 0 0K 4912K swapin 0 1:04 0.00% kernel{swapper}
0 root -92 0 0K 4912K - 2 0:17 0.00% kernel{em0 que}
1767 root 20 0 57312K 10104K select 1 0:15 0.00% smbd
12 root -60 - 0K 528K WAIT 0 0:13 0.00% intr{swi4: clock}
643 dhcpd 20 0 24524K 13044K select 1 0:07 0.00% dhcpd
12 root -88 - 0K 528K WAIT 1 0:04 0.00% intr{irq259: ahci0:ch}
14 root -16 - 0K 16K - 2 0:04 0.00% rand_harvestq
58515 jdc 20 0 37028K 6196K select 2 0:03 0.00% sshd
420 bind 20 0 70872K 36552K kqread 0 0:02 0.00% named{named}
19 root 20 - 0K 16K sdflus 2 0:02 0.00% softdepflush
420 bind 20 0 70872K 36552K uwait 3 0:02 0.00% named{named}
This is with a system uptime of 14 hours.
Comparatively, the RELENG_9 box I have (although it's on a VPS), which
does a lot more in general and has an uptime of 39 days, shows something
like this:
PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU COMMAND
12 root -60 - 0K 224K WAIT 0 132:49 0.00% intr{swi4: clock}
0 root -92 0 0K 160K - 0 89:01 0.00% kernel{em0 taskq}
17 root 16 - 0K 16K syncer 0 45:46 0.00% syncer
12 root -88 - 0K 224K WAIT 1 16:31 0.00% intr{irq14: ata0}
12 root -60 - 0K 224K WAIT 1 12:52 0.00% intr{swi4: clock}
13 root -8 - 0K 48K - 1 8:03 0.00% geom{g_down}
15490 halbot 20 0 76172K 22532K select 0 6:34 0.00% perl
593 bind 20 0 92288K 23740K uwait 1 4:39 0.00% named{named}
593 bind 20 0 92288K 23740K uwait 0 4:36 0.00% named{named}
So syncer looks like it might be about right for both systems, but
"swapper" (still not sure what that is exactly) sure seems to be much
more busy on the RELENG_10 box doing nothing vs. the RELENG_9 box.
Here's the swapper line from the RELENG_9 box:
$ top -a -H -S -b 9999 | grep swapper
0 root -16 0 0K 160K swapin 0 0:55 0.00% kernel{swapper}
It's the only suspect I have at this point but it's not very good
evidence of anything. :/
Maybe I can use while : ; do top -a -S -H -z -b 99999 >> somelog.txt ;
sleep 0.25 ; done and let that run for a while in hopes of catching
something? But I also worry that such a test would actually impact the
load itself.
On Sun, Jul 20, 2014 at 03:26:02PM +0100, Steven Hartland wrote:
> If you add -H -z to your top command does anything stand out?
>
> Regards
> Steve
> ----- Original Message -----
> From: "Jeremy Chadwick" <jdc at koitsu.org>
> To: <freebsd-stable at freebsd.org>
> Sent: Sunday, July 20, 2014 7:24 AM
> Subject: Consistently "high" CPU load on 10.0-STABLE
>
>
> > (Please keep me CC'd as I'm not subscribed to freebsd-stable@)
> >
> > Today I took the liberty of upgrading my main home server from
> > 9.3-STABLE (r268785) to 10.0-STABLE (r268894). The upgrade consisted of
> > doing a fresh install of 10.0-STABLE on a brand new unused SSD. Most
> > everything went as planned, barring a couple ports-related anomalies,
> > and I seemed fairly impressed by the fact that buildworld times had
> > dropped to 27 minutes and buildkernel to 4 minutes with clang (something
> > I'd been avoiding like the plague for a long while). Kudos.
> >
> > But after an hour or so, I noticed a consistent (i.e. reproducible)
> > trend: the system load average tends to hang around 0.10 to 0.15 all the
> > time. There are times where the load drops to 0.03 or 0.04 but then
> > something kicks it back up to 0.15 or 0.20 and then it slowly levels out
> > again (over the course of a few minutes) then repeats.
> >
> > Obviously this is normal behaviour for a system when something is going
> > on periodically. So I figured it might have been a userland process
> > behaving differently under 10.x than 9.x. I let top -a -S -s 1 run and
> > paid very very close attention to it for several minutes. Nothing. It
> > doesn't appear to be something userland -- it appears to be something
> > kernel-level, but nothing in top -S shows up as taking up any CPU time
> > other than "[idle]" so I have no idea what might be doing it.
> >
> > The box isn't doing anything like routing network traffic/NAT, it's pure
> > IPv4 (IPv6 disabled in world and kernel, and my home network does
> > basically no IPv6) and sits idle most of the time fetching mail. It
> > does use ZFS, but not for /, swap, /var, /tmp, or /usr.
> >
> > vmstat -i doesn't particularly show anything awful. All the cpuX:timer
> > entries tend to fluctuate in rate, usually 120-200 or so; I'd expect an
> > interrupt storm to be showing something in the 1000+ range.
> >
> > The only thing I can think of is the fact that the SSD being used has no
> > 4K quirk entry in the kernel (and its ATA IDENTIFY responds with 512
> > logical, 512 physical, even though we know it's 4K). The partitions are
> > all 1MB-aligned regardless.
> >
> > This is all bare-metal, by the way -- no virtualisation involved.
> >
> > I do have DTrace enabled/built on this box but I have absolutely no clue
> > how to go about profiling things. For example maybe output of this sort
> > would be helpful (but I've no idea how to get it):
> >
> > http://lists.freebsd.org/pipermail/freebsd-stable/2014-July/079276.html
> >
> > I'm certain I didn't see this behaviour in 9.x so I'd be happy to try
> > and track it down if I had a little bit of hand-holding.
> >
> > I've put all the things I can think of that might be relevant to "system
> > config/tuning bits" up here:
> >
> > http://jdc.koitsu.org/freebsd/releng10_perf_issue/
> >
> > I should note my kernel config is slightly inaccurate (I've removed some
> > stuff from the file in attempt to rebuild, but building world prior to
> > kernel failed due to r268896 breaking world, but anyone subscribed here
> > has already seen the Jenkins job of that ;-) ).
> >
> > Thanks.
> >
> > --
> > | Jeremy Chadwick jdc at koitsu.org |
> > | UNIX Systems Administrator http://jdc.koitsu.org/ |
> > | Making life hard for others since 1977. PGP 4BD6C0CB |
> >
> > _______________________________________________
> > freebsd-stable at freebsd.org mailing list
> > http://lists.freebsd.org/mailman/listinfo/freebsd-stable
> > To unsubscribe, send any mail to "freebsd-stable-unsubscribe at freebsd.org"
> >
--
| Jeremy Chadwick jdc at koitsu.org |
| UNIX Systems Administrator http://jdc.koitsu.org/ |
| Making life hard for others since 1977. PGP 4BD6C0CB |
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