lkml.org 
[lkml]   [2015]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [Xen-devel] linux 4.4 Regression: 100% cpu usage on idle pv guest under Xen with single vcpu.
From
Date
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

>
> --
> Sander
>
>>
>> -boris
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel



\
 
 \ /
  Last update: 2015-12-02 00:41    [W:0.051 / U:0.520 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site