[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [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

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

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:

static inline int nr_legacy_irqs(void)
        return legacy_pic->nr_legacy_irqs;

returns something different in some circumstances ?



Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.