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Message-ID: <20090324114715.GC6058@nowhere> Date: Tue, 24 Mar 2009 12:47:15 +0100 From: Frederic Weisbecker <fweisbec@...il.com> To: Kevin Shanahan <kmshanah@...b.org.au> Cc: Avi Kivity <avi@...hat.com>, "Rafael J. Wysocki" <rjw@...k.pl>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Kernel Testers List <kernel-testers@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: [Bug #12465] KVM guests stalling on 2.6.28 (bisected) On Tue, Mar 24, 2009 at 12:44:12PM +0100, Frederic Weisbecker wrote: > On Sat, Mar 21, 2009 at 03:30:39PM +1030, Kevin Shanahan wrote: > > On Thu, 2009-03-19 at 07:54 +1030, Kevin Shanahan wrote: > > > On Wed, 2009-03-18 at 11:46 +1030, Kevin Shanahan wrote: > > > > On Wed, 2009-03-18 at 01:20 +0100, Frederic Weisbecker wrote: > > > > > Ok, I've made a small script based on yours which could do this job. > > > > > You will just have to set yourself a threshold of latency > > > > > that you consider as buggy. I don't remember the latency you observed. > > > > > About 5 secs right? > > > > > > > > > > It's the "thres" variable in the script. > > > > > > > > > > The resulting trace should be a mixup of the function graph traces > > > > > and scheduler events which look like this: > > > > > > > > > > gnome-screensav-4691 [000] 6716.774277: 4691:120:S ==> [000] 0:140:R <idle> > > > > > xfce4-terminal-4723 [001] 6716.774303: 4723:120:R + [001] 4289:120:S Xorg > > > > > xfce4-terminal-4723 [001] 6716.774417: 4723:120:S ==> [001] 4289:120:R Xorg > > > > > Xorg-4289 [001] 6716.774427: 4289:120:S ==> [001] 0:140:R <idle> > > > > > > > > > > + is a wakeup and ==> is a context switch. > > > > > > > > > > The script will loop trying some pings and will only keep the trace that matches > > > > > the latency threshold you defined. > > > > > > > > > > Tell if the following script work for you. > > > > > > ... > > > > > > > Either way, I'll try to get some results in my maintenance window > > > > tonight. > > > > > > Testing did not go so well. I compiled and booted > > > 2.6.29-rc8-tip-02630-g93c4989, but had some problems with the system > > > load when I tried to start tracing - it shot up to around 16-20 or so. I > > > started shutting down VMs to try and get it under control, but before I > > > got back to tracing again the machine disappeared off the network - > > > unresponsive to ping. > > > > > > When I got in this morning, there was nothing on the console, nothing in > > > the logs to show what went wrong. I will try again, but my next chance > > > will probably be Saturday. Stay tuned. > > > > Okay, new set of traces have been uploaded to: > > > > http://disenchant.net/tmp/bug-12465/trace-3/ > > > > These were done on the latest tip, which I pulled down this morning: > > 2.6.29-rc8-tip-02744-gd9937cb. > > > > The system load was very high again when I first tried to trace with > > sevarl guests running, so I ended up only having the one guest running > > and thankfully the bug was still reproducable that way. > > > > Fingers crossed this set of traces is able to tell us something. > > > > Regards, > > Kevin. > > > > > > Sorry, I've been late to answer. > As I explained in my previous mail, you trace is only > a snapshot that happened in 10 msec. > > I experimented different sizes for the ring buffer but even > a 1 second trace require 20 Mo of memory. And a so huge trace > would be impractical. > > I think we should keep the trace filters we had previously. > If you don't minde, could you please retest against latest -tip > the following updated patch? Iadded the filters, fixed the python > subshell and also flushed the buffer more nicely according to > a recent feature in -tip: > > echo > trace > > instead of switching to nop. > You will need to pull latest -tip again. > > Thanks a lot Kevin! Ah you will also need to increase the size of your buffer. See below: > > #!/bin/bash > > # Switch off all CPUs except for one to simplify the trace > echo 0 > /sys/devices/system/cpu/cpu1/online > echo 0 > /sys/devices/system/cpu/cpu2/online > echo 0 > /sys/devices/system/cpu/cpu3/online > > > # Make sure debugfs has been mounted > if [ ! -d /sys/kernel/debug/tracing ]; then > mount -t debugfs debugfs /sys/kernel/debug > fi > > # Set up the trace parameters > pushd /sys/kernel/debug/tracing || exit 1 > echo 0 > tracing_enabled > echo function_graph > current_tracer > echo funcgraph-abstime > trace_options > echo funcgraph-proc > trace_options > > # Set here the kvm IP addr > addr="hermes-old" > > # Set here a threshold of latency in sec > thres="5000" > found="False" > lat=0 > prefix=/sys/kernel/debug/tracing > > echo 1 > $prefix/events/sched/sched_wakeup/enable > echo 1 > $prefix/events/sched/sched_switch/enable > > # Set the filter for functions to trace > echo '' > set_ftrace_filter # clear filter functions > echo '*sched*' >> set_ftrace_filter > echo '*wake*' >> set_ftrace_filter > echo '*kvm*' >> set_ftrace_filter > > # Reset the function_graph tracer > echo function_graph > $prefix/current_tracer Put a echo 20000 > $prefix/buffer_size_kb So that we will have enough space (hopefully). Thanks! > > while [ "$found" != "True" ] > do > # Flush the previous buffer > echo trace > $prefix/trace > > echo 1 > $prefix/tracing_enabled > lat=$(ping -c 1 $addr | grep rtt | grep -Eo " [0-9]+.[0-9]+") > echo 0 > $prefix/tracing_enabled > > echo $lat > found=$(python -c "print float(str($lat).strip())") > sleep 0.01 > done > > echo 0 > $prefix/events/sched/sched_wakeup/enable > echo 0 > $prefix/events/sched/sched_switch/enable > > > echo "Found buggy latency: $lat" > echo "Please send the trace you will find on $prefix/trace" > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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