utilising multicoreprocessor support in linux 2286

On Monday 28 August 2006 11:01, Tom Forsmo stood up and addressed the mbuttes incomp.os.linux.miscas follows...:

Perhaps you should have set it up for 4 processors, because if those cores are hyperthreaded - and provided that hyperthreading is enabled in the BIOS and that you're running an ACPI interpreter - then you have 4 logical CPU's.

topnormally defaults to showing a non-SMP view. You should press "1" to enable an SMP view.

2.2 and 2.4 Linux kernel generations are by default not good choices for hyperthreaded or multi-core CPU's in physical SMP set-ups because they don't normally distinguish between a physical CPU and a hyperthreaded sibling or an on-chip second core, which leads to poor load balancing and may cause one physical CPU to generate more heat and do all the work when another physical CPU is completely idle.

I would advise sticking to a 2.6 kernel for such a machine.

The kernel will dispatch processes across the available CPU cores-hyperthreads as it sees fit, but in order to take advantage of true multi-threading, your application software itself has to support it.

If it doesn't, then the kernel can run process abc on one CPU and process xyz on another one, but those will then be the entire processes. Threads are also being used but are only implemented at the kernel level, i.e. for kernelspace processes.

If you want your userspace processes to support threads - and to thus execute faster on a multi-threaded machine - you'll have to compile them with thread support. Older GNU-Linux distributions make use of the so-called Linux Threads (LT), while newer distributions make use of the Native POSIX Threads for Linux (NPTL), with or without support for the older Linux Threads.

An example of an application that usually supports threads is The Gimp, and KVIrc - an excellent Qt-based IRC client - also supports threads.

Your Google's as good as mine... ;-)

-- With kind regards,

*Aragorn* (registered GNU-Linux user #223157)