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Christian_Gebau's avatar
Christian_Gebau
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Jul 12, 2006

iRule optimization / CPU usage monitor

Hi,

I am currently evaluating a BIG-IP load balancer. My goal is to

distribute incoming UDP packets (which conform to a custom network

protocol) to a cluster of linux servers. I use the round-robin

load balancing algorithm and no session persistance.

The load balancer has to execute an iRule for each incoming

packet in order to insert a sequence number into the UDP payload.

With my current setup I can handle about 20000 packets per second

on a BIG-IP 5100. Without the iRule the same box can handle up to

80000 packets/sec, therefore I would like to optimize my iRule.

Question 1)

Do you have any suggestions how I can speed the following iRule:


when RULE_INIT {
  array unset sequence_number_map
  array set sequence_number_map { }    
}
when CLIENT_DATA {
  global sequence_number_map
  if { [UDP::payload length] > 4} {
    binary scan [UDP::payload] II liid seid
    if {[catch {set sequence_number [lindex $sequence_number_map($liid,$seid) 0]}]} {
      set sequence_number 0
    }
    else
    {
      incr sequence_number
    }
    set sequence_number_map($liid,$seid) [list $sequence_number [clock seconds]]
    UDP::payload replace 0 0 [binary format I  $sequence_number]
   }
}

(The time stamp value in the sequence number map is used by another iRule that

removes obsolete entries in the map)

Question 2)

The web interface indicates that the TMM CPU usage doesn't exceed 50% during

my performance tests. Is this the normal behaviour? I would have expected values up

to 100%.

Best Regards,

Christian Gebauer
application delivery
dev
devops
iRules

3 Replies

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  • unRuleY_95363's avatar
    unRuleY_95363
    Historic F5 Account
    Jul 12, 2006
    What version are you running?

     

     

    The [clock seconds] command can be detrimental to performance prior to v9.2. Have you tried removing that since I don't see where you even reference that index of the list (I'm not sure why you are even using a list since you only seem to utilize the sequence number in position 0). Perhaps that was something you haven't utilized yet? Anyway, definitely try removing that and see if it helps. It doesn't sound like you are running into a bottleneck based on CPU load.
  • Christian_Gebau's avatar
    Christian_Gebau
    Icon for Nimbostratus rankNimbostratus
    Jul 13, 2006
    Hi,

     

     

    we are using "BIG-IP 9.2.3 Build 34.4"

     

     

    The reason for storing the current time stamp in the map with the sequence numbers is that we have to remove obsolete items from this map at some point in time. Its not possible to detect the end of a session/connection by parsing the content of the UDP packets so we have to rely on removing entries after some timeout. We plan to do this cleanup in a different iRule (because the timer event is not yet available)

     

     

    I removed the list/timestamp code and did a test. If I just store the sequence number the rule uses an average of 32600 cpu cycles. This is not much lower than the value for the original rule (35500 cycles). The worst offenders seem to be the two commands for reading and writing the UDP payload. A rule that just contains the "binary scan" and "payload replace" commands uses 21300 cycles.

     

     

    Best Regards,

     

    Christian
    • pirusti's avatar
      pirusti
      Icon for Nimbostratus rankNimbostratus
      Jan 25, 2019

      how do you manage to get those numbers, i mean how do you measure the cpu cycles that an iRules uses.