a final few more features in stress-ng

While hoping to get a feature complete stress-ng sooner than later, I found a few more ways to fiendishly stress a system.

Stress-ng 0.01.22 will be landing soon in Ubuntu 14.10 with three more stress mechanisms:

• CPU affinity stressing; this rapidly changes CPU affinity of the stress processes just to keep the scheduling busy wasting effort.
• Timer stressing using the real-time clock; this allows one to generate a large amount of timer interrupts, so it is a useful interrupt saturation test.
• Directory entry thrashing; this creates and deletes a selectable number of zero length files and hence populates and destroys directory entries.

I have also removed the need to use rand() for random number generation for some of the stress tests and re-used a the faster MWC "random" number generator to add in some well known and very simple math operations for CPU stressing.

Stress-ng now has 15 different simple stress mechanisms that exercise CPU, cache, memory, file system, I/O and CPU schedulers.  I could add more tests, but I think this is a large enough set to allow one to thrash a machine and see how well it performs under pressure.

more stress with stress-ng

Since my last article about stress-ng I have been adding a few more stress mechanisms to stress-ng:

• file locking - exercise file locking with one or more processes (the more processes the better).
• fallocate - this allocates a 4MB file, sync's, truncates to zero size and syncs repeatedly
• yield - this loops on sched_yield() to repeatedly relinquish the CPU forcing a high context switch rate when run with multiple yielding processes.

Also, I have added some new features to tweak scheduling, I/O characteristics and memory allocations of the running stress processes:

• --sched and --sched-prio options to specify the scheduler type and priority
• --ionice-class and --ionice-level options to tweak I/O niceness
• --vm-populate option to populate (pre-fault) page tables for a mapping for the --vm stress test.

If I think of other mechanisms to stress the kernel I will add them, but for now, stress-ng is becoming almost feature complete.

idlestat: a tool to measure times in idle and operational states

Linaro's idlestat is another useful tool in the arsenal of CPU monitoring utilities.  Idlestat monitors and captures CPU C-state and P-state transitions using the kernel Ftrace tracer and outputs statistics based on entering/exiting each state for each CPU.  Idlestat  also captures IRQ activity as well which ones caused a CPU to exit an idle state -  knowing why a processor came out of a deep C state is always very useful way to help diagnose power consumption issues.

Using idlestat is easy, to capture 20 seconds of activity into a log file called example.log, run:

 sudo idlestat --trace -f example.log -t 20    

..and this will display the per CPU C-state and P-state and IRQ statistics for that run.

One can also take the saved log file and parse it again to calculate the statistics again using:

 idlestat --import -f example.log  

One can get the source from here and I've packaged version 0.3 (plus a bunch of minor fixes that will land in 0.4) for Ubuntu 14.10 Utopic Unicorn.

stress-ng: an updated system stress test tool

Recently added to Ubuntu 14.10 is stress-ng, a simple tool designed to stress various components of a Linux system.   stress-ng is a re-implementation of the original stress tool written by Amos  Waterland and adds various new ways to exercise a computer as well as a very simple "bogo-operation" set of metrics for each stress method.

stress-ng current contains the following methods to exercise the machine:

• CPU compute - just lots of sqrt() operations on pseudo-random values. One can also specify the % loading of the CPUs
• Cache thrashing, a naive cache read/write exerciser
• Drive stress by writing and removing many temporary files
• Process creation and termination, just lots of fork() + exit() calls
• I/O syncs, just forcing lots of sync() calls
• VM stress via mmap(), memory write and munmap()
• Pipe I/O, large pipe writes and reads that exercise pipe, copying and context switching
• Socket stressing, much like the pipe I/O test but using sockets
• Context switching between a pair of producer and consumer processes

Many of the above stress methods have additional configuration options.  Each stress method can be run by one or more child processes.

The --metrics option dumps the number of operations performed by each stress method, aka "bogo ops", bogos because they are a rough and unscientific metric.  One can specify how long to run a test either by test duration in sections or by bogo ops.

I've tried to make stress-ng compatible with the older stress tool, but note that it is not guaranteed to produce identical results as the common test methods between the two tools have been implemented differently.

Stress-ng has been a useful for helping me measure different power consuming loads.  It is also useful with various thermald optimisation tweaks on one of my older machines.

For more information, consult the stress-ng manual page.  Be warned, this tool can make your system get seriously busy and warm!