From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dong Liu <dliu.cn@gmail.com>
Subject: Re: cpu stall and hyperthread
Date: Fri, 06 Jul 2012 12:03:37 -0400
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References: <4FEBCDDE.60503@gmail.com> <4FF68396.2010904@gmail.com> <4FF6CEA6.6080900@osadl.org>
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To: Carsten Emde <C.Emde@osadl.org>
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On 7/6/12 7:40 AM, Carsten Emde wrote:
> Hi Dong,
>
>> I can quite reliably trigger this cpu stall error now. Just try to start
>> several KVM guests.
> Good. BTW, we do repeated long-term tests 14 times per day with a single
> kvm guest that runs on two cores and conducts a number of CPU
> benchmarks. (https://www.osadl.org/?id=931) - never had this problem. So
> it may be related to running more than a single kvm guest.
>

I'm using i7 860 with HT enabled. It has 8 logical cores. Maybe it has 
something to do with it.
>> [..]
>> Are there any way I can use to narrow down this error?
> cd /sys/kernel/debug/tracing/
> echo 0 >tracing_on
> echo 1 >events/enable
> echo function >current_tracer
> echo 14080 >buffer_size_kb
> echo 1 >tracing_on
> while true
> do
> if dmesg | tail -100 | grep -q "rcu_preempt detected stalls"
> then
> echo 0 >tracing_on
> break
> fi
> sleep 1
> done

I don't have /sys/kernel/debug/tracing/ directory. The kernel doc says 
turn on CONFIG_KPROBE_TRACING. But I could not find this config.


>
> Then start the kvm quests.
>
> Alternatively, you may use the kernel parameter ftrace_dump_on_oops.
>
I'll try that.

Thanks,

Dong