Bulat Ziganshin wrote:
Monday, December 22, 2008, 11:07:32 PM, you wrote:
The threaded RT creates an OS thread for each CPU/core on the system and uses them to multiplex userland threads. These are context switched whenever they block/yield/gc and no priorities can be assigned.
not exactly. amount of OS threads created controlled by +RTS -N option to the program; unless program has special function that RTS calls to set up this value
There might be multiple OS threads per CPU, if for example one of the Haskell threads makes a safe foreign call another OS thread takes over running the rest of the Haskell threads on that CPU. When you say "+RTS -N2" all you are saying is "I want to allow up to 2 Haskell threads to run simultaneously". The actual mapping between Haskell threads and OS threads is decided by the RTS, hopefully in a sensible way, within this constraint.
they are switched on every minor GC which by default occurs after each 256kb allocated which is rather frequent event
512Kb by default (caches are bigger these days), and configurable with +RTS -A<size>. Cheers, Simon