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Date: Wed, 02 Dec 2015 00:44:54 +0100
From: Sander Eikelenboom <linux@...elenboom.it>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xen.org,
david.vrabel@...rix.com
Subject: Re: [Xen-devel] linux 4.4 Regression: 100% cpu usage on idle pv
guest under Xen with single vcpu.
On 2015-12-02 00:41, Boris Ostrovsky wrote:
> On 12/01/2015 06:30 PM, Sander Eikelenboom wrote:
>> On 2015-12-02 00:19, Boris Ostrovsky wrote:
>>> On 12/01/2015 06:00 PM, Sander Eikelenboom wrote:
>>>> On 2015-12-01 23:47, Boris Ostrovsky wrote:
>>>>> On 11/30/2015 05:55 PM, Sander Eikelenboom wrote:
>>>>>> On 2015-11-30 23:54, Boris Ostrovsky wrote:
>>>>>>> On 11/30/2015 04:46 PM, Sander Eikelenboom wrote:
>>>>>>>> On 2015-11-30 22:45, Konrad Rzeszutek Wilk wrote:
>>>>>>>>> On Sat, Nov 28, 2015 at 04:47:43PM +0100, Sander Eikelenboom
>>>>>>>>> wrote:
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> I have just tested a 4.4-rc2 kernel (current linus tree) + the
>>>>>>>>>> tip tree
>>>>>>>>>> pulled on top.
>>>>>>>>>>
>>>>>>>>>> Running this kernel under Xen on PV-guests with multiple vcpus
>>>>>>>>>> goes well (on
>>>>>>>>>> idle < 10% cpu usage),
>>>>>>>>>> but a guest with only a single vcpu doesn't idle at all, it
>>>>>>>>>> seems a kworker
>>>>>>>>>> thread is stuck:
>>>>>>>>>> root 569 98.0 0.0 0 0 ? R 16:02 12:47
>>>>>>>>>> [kworker/0:1]
>>>>>>>>>>
>>>>>>>>>> Running a 4.3 kernel works fine with a single vpcu, bisecting
>>>>>>>>>> would probably
>>>>>>>>>> quite painful since there were some breakages this merge
>>>>>>>>>> window with respect
>>>>>>>>>> to Xen pv-guests.
>>>>>>>>>>
>>>>>>>>>> There are some differences in the diff's from booting a 4.3,
>>>>>>>>>> 4.4-single,
>>>>>>>>>> 4.4-multi cpu boot:
>>>>>>>>>
>>>>>>>>> Boris has been tracking a bunch of them. I am attaching the
>>>>>>>>> latest set of
>>>>>>>>> patches I've to carry on top of v4.4-rc3.
>>>>>>>>
>>>>>>>> Hi Konrad,
>>>>>>>>
>>>>>>>> i will test those, see if it fixes all my issues and report back
>>>>>>>
>>>>>>> They shouldn't help you ;-( (and I just saw a message from you
>>>>>>> confirming this)
>>>>>>>
>>>>>>> The first one fixes a 32-bit bug (on bare metal too). The second
>>>>>>> fixes
>>>>>>> a fatal bug for 32-bit PV guests. The other two are code
>>>>>>> improvements/cleanup.
>>>>>>
>>>>>> One of these patches also fixes a bug i was having with a
>>>>>> pci-passthrough device in
>>>>>> a HVM that wasn't working (depending on which dom0-kernel i was
>>>>>> using (4.3 or 4.4)),
>>>>>> but didn't report yet.
>>>>>>
>>>>>> Fingers crossed but i think this pv-guest single vcpu issue is the
>>>>>> last i'm troubled by for now ;)
>>>>>
>>>>> I could not reproduce this, including with your kernel config file.
>>>>
>>>> Hmm that's unpleasant :-\
>>>>
>>>> Hmm other strange thing is it doesn't seem to affect dom0 (which is
>>>> also a PV guest), but only unprivileged ones
>>>> All unprivileged pv-guests seem to have the irq issue, but only with
>>>> a single vcpu i see to get the stuck kworker thread that got my
>>>> attention, with a 2 vcpu that doesn't seem to happen, but you still
>>>> get the dmesg output and warnings about hvc)
>>>>
>>>> Could it be that:
>>>>
>>>> arch/x86/include/asm/i8259.h
>>>> static inline int nr_legacy_irqs(void)
>>>> {
>>>> return legacy_pic->nr_legacy_irqs;
>>>> }
>>>>
>>>> returns something different in some circumstances ?
>>>
>>> It should return 16 pre-8c058b0b9c34d8c8d7912880956543769323e2d8 and
>>> 0
>>> after that commit.
>>>
>>> This is the last number that you see in
>>> NR_IRQS:4352 nr_irqs:48 0
>>> line.
>>>
>>> I think you should be able to safely revert both
>>> b4ff8389ed14b849354b59ce9b360bdefcdbf99c and
>>> 8c058b0b9c34d8c8d7912880956543769323e2d8 and see if it makes any
>>> difference.
>>>
>>>
>>> -boris
>>>
>>
>> That was already underway compiling :)
>>
>> And it does reveal that reverting both fixes the issue, no stuck
>> kworker thread .. and no:
>> genirq: Flags mismatch irq 8. 00000000 (hvc_console) vs. 00000000
>> (rtc0)
>> hvc_open: request_irq failed with rc -16.
>
>
> Let me try it again tomorrow. Can you post your guest config file, Xen
> version and host HW (Intel or AMD)? 'xl info' maybe?
>
> -boris
Guest config file == dom0 config file == the one i send you earlier.
Host is an AMD Phenom X6.
# xl info
host : serveerstertje
release : 4.4.0-rc3-20151201-linus-doflr-boris+
version : #1 SMP Tue Dec 1 19:02:58 CET 2015
machine : x86_64
nr_cpus : 6
max_cpu_id : 5
nr_nodes : 1
cores_per_socket : 6
threads_per_core : 1
cpu_mhz : 3200
hw_caps :
178bf3ff:efd3fbff:00000000:00011300:00802001:00000000:000037ff:00000000
virt_caps : hvm hvm_directio
total_memory : 20479
free_memory : 7745
sharing_freed_memory : 0
sharing_used_memory : 0
outstanding_claims : 0
free_cpus : 0
xen_major : 4
xen_minor : 7
xen_extra : -unstable
xen_version : 4.7-unstable
xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
hvm-3.0-x86_32p hvm-3.0-x86_64
xen_scheduler : credit
xen_pagesize : 4096
platform_params : virt_start=0xffff800000000000
xen_changeset : Thu Nov 26 20:58:13 2015 +0100
git:5252636-dirty
xen_commandline : dom0_mem=1536M,max:1536M loglvl=all
loglvl_guest=all console_timestamps=datems vga=gfx-1280x1024x32 cpuidle
cpufreq=xen com1=38400,8n1 console=vga,com1 ivrs_ioapic[6]=00:14.0
iommu=on,verbose,debug,amd-iommu-debug conring_size=128k ucode=-1
cc_compiler : gcc-4.9.real (Debian 4.9.2-10) 4.9.2
cc_compile_by : root
cc_compile_domain : dyndns.org
cc_compile_date : Thu Nov 26 21:18:41 CET 2015
xend_config_format : 4
If you need and can get more info by letting me run a debug patch for
you (because you can't reproduce) don't hesitate to send one :)
Thanks so far !
--
Sander
>
>
>>
>> What i did get was an conflict reverting
>> b4ff8389ed14b849354b59ce9b360bdefcdbf99c:
>> arch/arm64/include/asm/irq.h, although that shouldn't matter because
>> we are on x86 and not on arm.
>>
>> -- Sander
>>
>>
>>>>
>>>> -- Sander
>>>>
>>>>>
>>>>> -boris
>>>>
>>>> _______________________________________________
>>>> Xen-devel mailing list
>>>> Xen-devel@...ts.xen.org
>>>> http://lists.xen.org/xen-devel
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