Multitasking on Linux with multiple CPUs

I feel my question is quite basic, but I couldn't find any related SO question.

I need to run a program a few thousands of times (different input each time), and currently it is done by a shell script. The machine runs Ubuntu and has 8 CPUs (as revealed by cat /proc/cpuinfo). Using top I see that only 1 CPU is utiliz开发者_JS百科ed. In order to speed thing up, I want to utilize all 8 CPUs. I know I can start the program in the background, and then call it again (and indeed top reveals that 2 CPUs are utilized in that case), so I can change my shell script to call the program in groups of 8. My question is, is that a recommended way to utilize all CPUs, or is there another, somewhat 'cleaner' way?

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You can use cpu affinity to be explicit about the processor for the processes.

http://www.cyberciti.biz/tips/setting-processor-affinity-certain-task-or-process.html

However, if each process runs on a cpu (as it should, the kernel will make sure that things are running as efficiently as possible), then just fire n processes off (8 in your case, or make your shell script figure out what n is so your script is a bit more robust, or make it a command line option) and let the kernel do it for you. Each time a process ends, fire off another process until you are done.

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Question is overly vague.

That you want to use all the CPUs implies you want the end result as quickly as possible - but a major concern for the performance f multiple instances would be contention for resources (reducing performance) and caching (improving performance).

Usually splitting the job amongst multiple processes will usually yield results faster. And there are many, many ways of sharding the workload. But without knowing a lot more about what it is doing it is difficult to recommend a particular approach.

Given that you have 8 CPUs, and assuming that the only constrained resource is the CPU, then you don't want to have more than 8 threads running concurrently on the job. So the problem then becomes how you schedule work to ensure that you are using the 8 cores optimally. Splitting the work into 8 scripts and running them concurrently you will initially see all 8 scripts running concurrently - but its very likely, depending on the nature of the work, that the scripts will finish at different times.

So if you really want to use the hardware optimally, that means running 8 processes as daemons, preferably with each process having a cpu affinity set, fed by a message queue. But is it really worthwhile coding all this if you're not going to be running this regularly? Also it may be faster to run just 7 and keep a CPU for handling the quueue and other demands placed on the box.