Tuesday, 29 October, 2013 22:09 Written by Brian B
The last blog post gave us some brief descriptions of the various scheduling classes in Solaris. I focused on the Time Sharing (TS) class since it is the default. Hopefully we can see that the TS (and the IA class for that matter) makes its decisions based on how the threads are using the CPU. Are we CPU intensive or are we I/O intensive? It works well, but it doesn’t provide the administrator fine-grain control as it relates to resource management.
To address this, The Fair Share Scheduler (FSS) was added to Solaris in the Solaris 9 release.
The primary benefit of FSS is to allow the admin an ability to identify and dispatch processes and their threads based upon their importance as determined by the business and implemented by the administrator.
We saw the complexity of the TS dispatch table in the earlier post. Here we see the FSS table has no such complexity.
In FSS we use the concept of CPU shares. These shares allow the admin a fine level of granularity to carve up CPU resources. We are no longer limited to allocating an entire CPU. The admin designates the importance of the workload by assigning to it a number of shares. You dictate importance by assigning a larger number of shares to those workloads that carry a higher importance. Shares ARE NOT the same as CPU caps nor CPU resource usage. Shares simply define the relative importance of workloads in comparison to other workloads where CPU resource usage is an actual measurement of consumption. A workload may be given 50% of the shares yet at a point in time may be only consuming 5% of the CPU. I look at a CPU share as a minimum guaranty of CPU allocation, not as a cap on CPU consumption.
When we assign shares to a work load, we need to be aware of the shares that are already assigned. It is the ratio of shares assigned to one workload compared to all of the other workloads.
I speak of FSS in a “Horizontal” and a “Vertical” aspect when I’m delivering for Oracle University. In Solaris 9 we were able to define projects in the /etc/project file. This is the vertical aspect. In Solaris 10 Non-Global Zones were introduced and brought with it the Horizontal aspect. I assign shares horizontally across the various zones and then vertically within each zone in the /etc/project file if needed.
By default the Non-Global zones use the default scheduling class. If the system is updated with a new default class, they will obtain the new setting when booted or rebooted. The recommended scheduler to use with Non-Global Zones is the FSS. The preferred way is to set the system default scheduler to FSS and all zones then inherit it.
To display information about the loaded scheduling classes, run priocntl -l
SYS (System Class)
TS (Time Sharing)
Configured TS User Priority Range: -60 through 60
SDC (System Duty-Cycle Class)
FX (Fixed priority)
Configured FX User Priority Range: 0 through 60
IA (Interactive)
Configured IA User Priority Range: -60 through 60
priocntl can be used to view or set scheduling parameters for a specified process.
To determine the global priority of a process run ps -ecl
root@solaris:~# ps -ecl #The c displays properties of the scheduler, we see the class (CLS) and the priority (PRI) F S UID PID PPID CLS PRI ADDR SZ WCHAN TTY TIME CMD 1 T 0 0 0 SYS 96 ? 0 ? 0:01 sched 1 S 0 5 0 SDC 99 ? 0 ? ? 0:02 zpool-rp 1 S 0 6 0 SDC 99 ? 0 ? ? 0:00 kmem_tas 0 S 0 1 0 TS 59 ? 720 ? ? 0:00 init 1 S 0 2 0 SYS 98 ? 0 ? ? 0:00 pageout 1 S 0 3 0 SYS 60 ? 0 ? ? 0:01 fsflush 1 S 0 7 0 SYS 60 ? 0 ? ? 0:00 intrd 1 S 0 8 0 SYS 60 ? 0 ? ? 0:00 vmtasks 0 S 0 869 1 TS 59 ? 1461 ? ? 0:05 nscd 0 S 0 11 1 TS 59 ? 3949 ? ? 0:11 svc.star 0 S 0 13 1 TS 59 ? 5007 ? ? 0:32 svc.conf 0 S 0 164 1 TS 59 ? 822 ? ? 0:00 vbiosd 0 S 16 460 1 TS 59 ? 1323 ? ? 0:00 nwamd
To set the default scheduling class use dispadmin -d FSS and then dispadmin -d to ensure it changed. Then run dispadmin -l to see that it loaded.
root@solaris:~# dispadmin -d dispadmin: Default scheduling class is not set root@solaris:~# dispadmin -d FSS root@solaris:~# dispadmin -d FSS (Fair Share) root@solaris:~# dispadmin -l CONFIGURED CLASSES ================== SYS (System Class) TS (Time Sharing) SDC (System Duty-Cycle Class) FX (Fixed Priority) IA (Interactive) FSS (Fair Share)
Manually move add of the running processes into the FSS class and then verify with the ps command.
root@solaris:~# priocntl -s -c FSS -i all root@solaris:~# ps -ef -o class,zone,fname | grep -v CLS | sort -k2 | more FSS global auditd FSS global automoun FSS global automoun FSS global bash FSS global bash FSS global bonobo-a FSS global clock-ap FSS global console- FSS global cron FSS global cupsd FSS global dbus-dae FSS global dbus-dae FSS global dbus-lau FSS global dbus-lau
Finally move init over to the FSS class so all children will inherit.
root@solaris:~# ps -ecf | grep init
root 1 0 TS 59 16:33:44 ? 0:00 /usr/sbin/init
root@solaris:~# priocntl -s -c FSS -i pid 1
root@solaris:~# ps -ecf | grep init
root 1 0 FSS 29 16:33:44 ? 0:00 /usr/sbin/init
With the FSS all set, we now assign shares to our Non-Global Zones
zonecfg -z
set cpu-shares=number of shares
exit zonecfg
To display CPU consumption run prstat -Z