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

--
Sander

>
> -boris


\
 
 \ /
  Last update: 2015-12-02 00:21    [W:0.042 / U:0.960 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site