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Here is a quick and easy way to tell if you have not allocated enough aioservers on your AIX 5.3 system. First you want to check how many you have configured currently:
$ lsattr -El aio0
autoconfig available STATE to be configured at system restart True fastpath enable State of fast path True kprocprio 39 Server PRIORITY True maxreqs 12288 Maximum number of REQUESTS True maxservers 120 MAXIMUM number of servers per cpu True minservers 80 MINIMUM number of servers True
The ‘maxservers’ setting on a 4 CPU system would give you a maximum count of 480 aioserver kernel threads. If SMT is enabled - which makes it appear as if each CPU is 2 CPUs - the maximum number of aioserver kernel threads would be 960 (480 * 2). You can check to see if SMT is enabled as root by using the smtctl(5) command - you can also enable or disable it with the same command. If you don’t have root access, you can also find out by using the lparstat command, seen below from a 4way LPAR:
$ lparstat
System configuration: type=Dedicated mode=Capped smt=On lcpu=8 mem=16384The ‘minservers’ setting is the total number of aioserver kernel threads that will start at boot - this is not a per CPU or per logical CPU value.
The ‘maxreqs’ setting is the maximum number of outstanding or pending requests that the kernel will allow at any one time.
aioserver kernel threads do not go away once started, until the system reboots. So, you can tell how many your applications have requested/required concurrently since boot by using the ps command:
$ ps -ek | grep aioserver | grep -v posix_aioserver | wc -l
960It appears that all 960 aioservers have been started, so sometime between when the system booted and this very instant, something needed all of them - and possibly more . The ‘-k’ argument to the ps command lists kernel threads (also known as kprocs) in addition to user-space processes.
Another test is to see how much CPU time each of the aioserver. If all of the aioserver threads have a very similar amount of CPU time, and if the amount of CPU time consumed is significant - chances are you need to configure more of them. Depending on how long the OS has been running, you may need to add quite a few more.
$ ps -ek | grep aioserver | more
118880 - 1:31 aioserver 127062 - 1:32 aioserver …You can change the AIO parameters for your system with the chdev command on the aio0 pseudo-device, or by running smitty aio on AIX 5.3 systems - you can even use the poorly documented aioo command. An important thing to remember though - is that you can set the values online, with no interruption of service - BUT - they will not take affect until the next time the kernel is booted.
Some additional documentation is available at the locations below:
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