Re: [Xen-devel] linux 4.4 Regression: 100% cpu usage on idle pv guest under Xen with single vcpu.

[Sander Eikelenboom <linux@eikelenboom.it>]

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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

Hi Boris,

A fresh new day .. a fresh new thought.
If i look at the /proc/interrupts from a broken and a kernel with both 
commits the
thing that catches the eye is irq8, just as the dmesg message was 
telling.

In my PV guest rtc0 now seems to try and take irq8 that was already 
assigned to HVC ?
Sounds like some assumptions around the legacy range are broken 
somewhere.

What is the benefit of not just reserving the legacy range ?

Attached the /proc/interrupts from both boots.

--
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@lists.xen.org
>>>> http://lists.xen.org/xen-devel

[-- Attachment #2: interrupts-after-reverts.txt --]
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           CPU0       
 16:     315536  xen-percpu-virq      timer0
 17:          0  xen-percpu-ipi       spinlock0
 18:          0  xen-percpu-ipi       resched0
 19:          0  xen-percpu-ipi       callfunc0
 20:          0  xen-percpu-virq      debug0
 21:          0  xen-percpu-ipi       callfuncsingle0
 22:          0  xen-percpu-ipi       irqwork0
 23:        346   xen-dyn-event     xenbus
 24:        134   xen-dyn-event     hvc_console
 25:      11464   xen-dyn-event     blkif
 26:      28710   xen-dyn-event     eth0-q0-tx
 27:      40136   xen-dyn-event     eth0-q0-rx
NMI:          0   Non-maskable interrupts
LOC:          0   Local timer interrupts
SPU:          0   Spurious interrupts
PMI:          0   Performance monitoring interrupts
IWI:          0   IRQ work interrupts
RTR:          0   APIC ICR read retries
RES:          0   Rescheduling interrupts
CAL:          0   Function call interrupts
TLB:          0   TLB shootdowns
TRM:          0   Thermal event interrupts
THR:          0   Threshold APIC interrupts
DFR:          0   Deferred Error APIC interrupts
MCE:          0   Machine check exceptions
MCP:          0   Machine check polls
ERR:          0
MIS:          0
PIN:          0   Posted-interrupt notification event
PIW:          0   Posted-interrupt wakeup event

[-- Attachment #3: interrupts-broken.txt --]
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           CPU0       
  0:      29053  xen-percpu-virq      timer0
  1:          0  xen-percpu-ipi       spinlock0
  2:          0  xen-percpu-ipi       resched0
  3:          0  xen-percpu-ipi       callfunc0
  4:          0  xen-percpu-virq      debug0
  5:          0  xen-percpu-ipi       callfuncsingle0
  6:          0  xen-percpu-ipi       irqwork0
  7:        342   xen-dyn-event     xenbus
  8:        140   xen-dyn-event     rtc0
  9:       3238   xen-dyn-event     blkif
 10:        119   xen-dyn-event     eth0-q0-tx
 11:        199   xen-dyn-event     eth0-q0-rx
NMI:          0   Non-maskable interrupts
LOC:          0   Local timer interrupts
SPU:          0   Spurious interrupts
PMI:          0   Performance monitoring interrupts
IWI:          0   IRQ work interrupts
RTR:          0   APIC ICR read retries
RES:          0   Rescheduling interrupts
CAL:          0   Function call interrupts
TLB:          0   TLB shootdowns
TRM:          0   Thermal event interrupts
THR:          0   Threshold APIC interrupts
DFR:          0   Deferred Error APIC interrupts
MCE:          0   Machine check exceptions
MCP:          0   Machine check polls
ERR:          0
MIS:          0
PIN:          0   Posted-interrupt notification event
PIW:          0   Posted-interrupt wakeup event