4.2. Prioritizing Network Traffic

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When running multiple network-related services on a single server system, it is important to define network priorities between these services. Defining these priorities ensures that packets originating from certain services have a higher priority than packets originating from other services. For example, such priorities are useful when a server system simultaneously functions as an NFS and Samba server. The NFS traffic must be of high priority as users expect high throughput. The Samba traffic can be deprioritized to allow better performance of the NFS server.
The net_prio subsystem can be used to set network priorities for processes in cgroups. These priorities are then translated into Type Of Service (TOS) bits and embedded into every packet. Follow the steps in Procedure 4.2, “Setting Network Priorities for File Sharing Services” to configure prioritization of two file sharing services (NFS and Samba).

Procedure 4.2. Setting Network Priorities for File Sharing Services

  1. The net_prio subsystem is not compiled in the kernel, it is a module that must be loaded manually. To do so, type:
    ~]# modprobe net_prio
  2. Attach the net_prio subsystem to the /cgroup/net_prio cgroup:
    ~]# mkdir /cgroup/net_prio
    ~]# mount -t cgroup -o net_prio net_prio /cgroup/net_prio
  3. Create two cgroups, one for each service:
    ~]# mkdir /cgroup/net_prio/nfs_high
    ~]# mkdir /cgroup/net_prio/samba_low
  4. To automatically move the nfs services to the nfs_high cgroup, add the following line to the /etc/sysconfig/nfs file:
    This configuration ensures that nfs service processes are moved to the nfs_high cgroup when the nfs service is started or restarted. For more information about moving service processes to cgroups, refer to Section 2.9.1, “Starting a Service in a Control Group”.
  5. The smbd daemon does not have a configuration file in the /etc/sysconfig directory. To automatically move the smbd daemon to the samba_low cgroup, add the following line to the /etc/cgrules.conf file:
    *:smbd                net_prio                samba_low
    Note that this rule moves every smbd daemon, not only /usr/sbin/smbd, into the samba_low cgroup.
    You can define rules for the nmbd and winbindd daemons to be moved to the samba_low cgroup in a similar way.
  6. Start the cgred service to load the configuration from the previous step:
    ~]# service cgred start
    Starting CGroup Rules Engine Daemon:                       [  OK  ]
  7. For the purposes of this example, let us assume both services use the eth1 network interface. Define network priorities for each cgroup, where 1 denotes low priority and 10 denotes high priority:
    ~]# echo "eth1 1" > /cgroup/net_prio/samba_low
    ~]# echo "eth1 10" > /cgroup/net_prio/nfs_high
  8. Start the nfs and smb services and check whether their processes have been moved into the correct cgroups:
    ~]# service smb start
    Starting SMB services:                                     [  OK  ]
    ~]# cat /cgroup/net_prio/samba_low
    ~]# service nfs start
    Starting NFS services:                                     [  OK  ]
    Starting NFS quotas:                                       [  OK  ]
    Starting NFS mountd:                                       [  OK  ]
    Stopping RPC idmapd:                                       [  OK  ]
    Starting RPC idmapd:                                       [  OK  ]
    Starting NFS daemon:                                       [  OK  ]
    ~]# cat /cgroup/net_prio/nfs_high
    Network traffic originating from NFS now has higher priority than traffic originating from Samba.
Similar to Procedure 4.2, “Setting Network Priorities for File Sharing Services”, the net_prio subsystem can be used to set network priorities for client applications, for example, Firefox.
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