linux-kernel - Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

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Date:	Thu, 22 Jan 2009 00:55:32 +1030
From:	Kevin Shanahan <kmshanah@...b.org.au>
To:	Avi Kivity <avi@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	bugme-daemon@...zilla.kernel.org
Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected)

On Tue, 2009-01-20 at 19:47 +0200, Avi Kivity wrote:
> Steven Rostedt wrote:
> > Note, the wakeup latency only tests realtime threads, since other threads
> > can have other issues for wakeup. I could change the wakeup tracer as
> > wakeup_rt, and make a new "wakeup" that tests all threads, but it may
> > be difficult to get something accurate.
> 
> Kevin, can you retest with kvm at realtime priority?

Running vanilla Linux 2.6.28, kvm-82. First a control test to check that
the problem is still there when running at normal priority:

--- hermes-old.wumi.org.au ping statistics ---
900 packets transmitted, 900 received, 0% packet loss, time 899283ms
rtt min/avg/max/mdev = 0.119/269.773/13739.426/1230.836 ms, pipe 14

Yeah, sure is.

Okay, so now I set the realtime attributes of the processes for the VM
instance being pinged:

flexo:~# ps ax | grep 6284
 6284 ?        Sl     6:11 /usr/local/kvm/bin/qemu-system-x86_64 -smp 2
-m 2048 -hda kvm-17-1.img -hdb kvm-17-tmp.img -net
nic,vlan=0,macaddr=52:54:00:12:34:67,model=rtl8139 -net
tap,vlan=0,ifname=tap17,script=no -vnc 127.0.0.1:17 -usbdevice tablet
-daemonize
flexo:~# pstree -p 6284
qemu-system-x86(6284)─┬─{qemu-system-x86}(6285)
                      ├─{qemu-system-x86}(6286)
                      └─{qemu-system-x86}(6540)

(info cpus on the QEMU console shows 6285 and 6286 being the VCPU
processes. Not sure what the third child is for, maybe vnc?.)

flexo:~# chrt -r -p 3 6284
flexo:~# chrt -r -p 3 6285
flexo:~# chrt -r -p 3 6286
flexo:~# chrt -p 6284
pid 6284's current scheduling policy: SCHED_RR
pid 6284's current scheduling priority: 3
flexo:~# chrt -p 6285
pid 6285's current scheduling policy: SCHED_RR
pid 6285's current scheduling priority: 3
flexo:~# chrt -p 6286
pid 6286's current scheduling policy: SCHED_RR
pid 6286's current scheduling priority: 3

And the result of the ping test now:

--- hermes-old.wumi.org.au ping statistics ---
900 packets transmitted, 900 received, 0% packet loss, time 899326ms
rtt min/avg/max/mdev = 0.093/0.157/3.611/0.117 ms

So, a _huge_ difference. But what does it mean?

Regards,
Kevin.

P.S. Can someone tell me if I'm doing the CC: to bugme-daemon wrong? I
     thought that was supposed to add the emails as comments to the
     bugzilla report?


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