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Bug 1740144

Summary: [RFE] Add visibility on vhost-user tx contention
Product: Red Hat Enterprise Linux Fast Datapath Reporter: David Marchand <dmarchan>
Component: openvswitch2.11Assignee: David Marchand <dmarchan>
Status: CLOSED CURRENTRELEASE QA Contact: Jean-Tsung Hsiao <jhsiao>
Severity: low Docs Contact:
Priority: unspecified    
Version: FDP 19.ECC: ctrautma, fbaudin, gmuthukr, jhsiao, kfida, qding, ralongi, vchundur
Target Milestone: ---   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: openvswitch2.11-2.11.0-28.el7fdn Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of:
: 1771390 (view as bug list) Environment:
Last Closed: 2020-01-28 22:09:06 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:

Description David Marchand 2019-08-12 11:14:03 UTC 
When multiple PMD threads in OVS want to push packets through a vhost-user port, but the virtual machine did not initialise enough queues, PMD threads have to take a lock on the queues.
This can result in packets losses because of the extra cost on handling the packets.

This behavior is hard to figure out without having a deep understanding on the platform, flows and PMD configurations.

Making this visible would help to debug these kinds of issues.
Comment 3 Jean-Tsung Hsiao 2019-11-27 04:16:56 UTC 
This RFE has been verified by the following test.

OVS-dpdk was running two queues, but testpmd on guest was running only one queue.

The following monitoring loop showed lots of vhost_tx_contention:

[root@netqe7 jhsiao]# while [ 1 ]; do ovs-appctl coverage/read-counter vhost_tx_contention; sleep 10; done
19540403
23171968
27235086
31227209
35301630
39423770
43134112
47094345
50820789
54727418

About 394,026 contentions in a second.
Comment 8 Jean-Tsung Hsiao 2019-11-29 00:37:30 UTC 
Verified using openvswitch2.11-2.11.0-28.el7fdn.x86_64:

[root@netqe7 jhsiao]# ovs-appctl coverage/show | grep vhost
vhost_tx_contention      51400.0/sec 92860.867/sec     4218.9417/sec   total: 15262537
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