Bug 1766917

Summary:	[RFE] _get_max_tap_queues does not make a distinction between vhostuser and tap
Product:	Red Hat OpenStack	Reporter:	Fabrizio Soppelsa <fsoppels>
Component:	openstack-nova	Assignee:	smooney
Status:	CLOSED DUPLICATE	QA Contact:	OSP DFG:Compute <osp-dfg-compute>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	13.0 (Queens)	CC:	dasmith, eglynn, fbaudin, jhakimra, kchamart, sbauza, sgordon, smooney, vromanso
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Last Closed:	2019-11-07 19:29:22 UTC	Type:	Bug
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Description Fabrizio Soppelsa 2019-10-30 09:38:26 UTC

Description of problem:
In code here: https://opendev.org/openstack/nova/src/branch/stable/train/nova/virt/libvirt/vif.py#L207-L241 the number of tap queues is determined:

            driver = 'vhost'
            max_tap_queues = self._get_max_tap_queues()

The function _get_max_tap_queues() returns a number based on the major kernel version.

There is no real distinction between the type of ports (i.e. vhostuser), so also for fast datapath on kernel 3, 8 will be returned anyway. "When the domain XML is written for the guest, vhost_queues is used in the 'queues' argument in the driver. When this value is >8, it fails when attempting to create the tap interface." and fails to start the VM[1].

We have a customer looking into the possibility of having more than 8 queues on fast datapath on kernel 3 (RHOSP 13).


Version-Release number of selected component (if applicable):
RHOSP 13, 14, 15


Additional info:
May qualify as RFE or NOTABUG if this scenario (> 8 queues, fast datapath) has been tested by us already with different combinations.

[1] https://access.redhat.com/solutions/3227911

Comment 2 smooney 2019-11-07 19:29:22 UTC


*** This bug has been marked as a duplicate of bug 1714075 ***