POD: soft lockups in dom0 kernel

[Dietmar Hahn <dietmar.hahn@ts.fujitsu.com>]

Hi,

when creating a bigger (> 50 GB) HVM guest with maxmem > memory we get
softlockups from time to time.

kernel: [  802.084335] BUG: soft lockup - CPU#1 stuck for 22s! [xend:31351]

I tracked this down to the call of xc_domain_set_pod_target() and further
p2m_pod_set_mem_target().

Unfortunately I can this check only with xen-4.2.2 as I don't have a machine
with enough memory for current hypervisors. But it seems the code is nearly
the same.

My suggestion would be to do the 'pod set target' in the function
xc_domain_set_pod_target() in chunks of maybe 1GB to give the dom0 scheduler
a chance to run.
As this is not performance critical it should not be a problem.

I can reproduce this with SLES11-SP3 with Linux 3.0.101 and xen-4.2.2.

# cat dummy
name = "DummyOS"
memory = 10000
maxmem = 12000
builder='hvm'

# echo 1 > /proc/sys/kernel/watchdog_thresh
# xm create -c dummy

This leads to a kernel message:
kernel: [ 5019.958089] BUG: soft lockup - CPU#4 stuck for 3s! [xend:20854]

Any comments are welcome.
Thanks.

Dietmar.

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