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
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