openstack
/
nova
Code Issues Proposed changes

libvirt: Increase incremental and max sleep time during device detach 

Bug #1894804 outlines how DEVICE_DELETED events were often missing from
QEMU on Focal based OpenStack CI hosts as originally seen in bug
 #1882521. This has eventually been tracked down to some undefined QEMU
behaviour when a new device_del QMP command is received while another is
still being processed, causing the original attempt to be aborted.

We hit this race in slower OpenStack CI envs as n-cpu rather crudely
retries attempts to detach devices using the RetryDecorator from
oslo.service. The default incremental sleep time currently being tight
enough to ensure QEMU is still processing the first device_del request
on these slower CI hosts when n-cpu asks libvirt to retry the detach,
sending another device_del to QEMU hitting the above behaviour.

Additionally we have also seen the following check being hit when
testing with QEMU >= v5.0.0. This check now rejects overlapping
device_del requests in QEMU rather than aborting the original:

cce8944cc9

This change aims to avoid this situation entirely by raising the default
incremental sleep time between detach requests from 2 seconds to 10,
leaving enough time for the first attempt to complete. The overall
maximum sleep time is also increased from 30 to 60 seconds.

Future work will aim to entirely remove this retry logic with a libvirt
event driven approach, polling for the the
VIR_DOMAIN_EVENT_ID_DEVICE_REMOVED and
VIR_DOMAIN_EVENT_ID_DEVICE_REMOVAL_FAILED events before retrying.

Finally, the cleanup of unused arguments in detach_device_with_retry is
left for a follow up change in order to keep this initial change small
enough to quickly backport.

Closes-Bug: #1882521
Related-Bug: #1894804
Change-Id: Ib9ed7069cef5b73033351f7a78a3fb566753970d
(cherry picked from commit dd1e6d4b0c)
This commit is contained in:
Lee Yarwood 2020-10-02 15:11:25 +01:00
parent 7baca2b1d1
commit 4819f694b2
1 changed files with 2 additions and 2 deletions
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4
nova/virt/libvirt/guest.py
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@ -367,8 +367,8 @@ class Guest(object):
return devs return devs
def detach_device_with_retry(self, get_device_conf_func, device, live, def detach_device_with_retry(self, get_device_conf_func, device, live,
max_retry_count=7, inc_sleep_time=2, max_retry_count=7, inc_sleep_time=10,
max_sleep_time=30, max_sleep_time=60,
alternative_device_name=None, alternative_device_name=None,
supports_device_missing_error_code=False): supports_device_missing_error_code=False):
"""Detaches a device from the guest. After the initial detach request, """Detaches a device from the guest. After the initial detach request,