[jboss-jira] [JBoss JIRA] (JGRP-2453) Change default TOS for UDP

[Dan Berindei (Jira)]

Dan Berindei created JGRP-2453:
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             Summary: Change default TOS for UDP
                 Key: JGRP-2453
                 URL: https://issues.redhat.com/browse/JGRP-2453
             Project: JGroups
          Issue Type: Enhancement
    Affects Versions: 4.0.22, 4.1.9
            Reporter: Dan Berindei
            Assignee: Bela Ban


The Linux kernel has some fairly sophisticated queueing disciplines like {{fq_codel}}, but the default one is {{pfifo_fast}}.

{quote}
pfifo_fast is like three tc-pfifo(8) queues side by side,
       where packets can be enqueued in any of the three bands based on
       their Type of Service bits or assigned priority.

       Not all three bands are dequeued simultaneously - as long as lower
       bands have traffic, higher bands are never dequeued. This can be used
       to prioritize interactive traffic or penalize 'lowest cost' traffic.
??[http://man7.org/linux/man-pages/man8/tc-pfifo_fast.8.html#ALGORITHM]??
{quote}

These are some examples of band mappings:

{quote}
{noformat}
TOS     Bits  Means                    Linux Priority    Band
------------------------------------------------------------
0x0     0     Normal Service           0 Best Effort     1
0x8     4     Maximize Throughput      2 Bulk            2
0x10    8     Minimize Delay           6 Interactive     0
0x18    12    mt+md                    4 Int. Bulk       1
{noformat}
??[http://man7.org/linux/man-pages/man8/tc-prio.8.html#QDISC_PARAMETERS]??
{quote}

By default {{UDP.tos="8"}}, which makes all UDP traffic go into band 2, lowest priority (bulk).
{{FD_ALL}} and {{FD_ALL2}} heartbeats are {{UDP}} traffic, and in some of our benchmarks there is enough 
client-server traffic in band 1 to delay the FD_ALL heartbeats for more than 10 seconds. 

We could either set the default TOS to {{0}} (best effort), or {{0x18}} (maximize throughput + minimize delay), the result is the same: band 1. 




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