On 12/29/2013 02:47 PM, "Ola Fosheim Grøstad"
<ola.fosheim.grostad+dl...@gmail.com>" wrote:
On Sunday, 29 December 2013 at 20:36:27 UTC, Walter Bright wrote:
I'll reiterate that the GC will NEVER EVER pause your program unless
you are actually calling the GC to allocate memory. A loop that does
not GC allocate WILL NEVER PAUSE.
That's fine, except when you have real-time threads.
I'm always astounded how often real-time anything gets thrown around.
Yeah sure, some programs are under time constraints. But from the way
everyone freaked out you'd think *all* programs are real-time.
But in fact it's a very small subset. Hell, it's small enough to be a
*special case*.
So unless you use non-temporal load/save in your GC traversal (e.g. on
x86 you have SSE instructions that bypass the cache), your GC might
trash the cache for other cores that run real-time threads which are
initiated as call-backs from the OS.
Awesome. So now to run a real-time application, you can't have any
program that uses a GC running on the same machine.
Somehow I don't think that is grounded in reality.
These callbacks might happen 120+ times per seconds and your runtime
cannot control those, they have the highest user-level priority.
Granted, the latest CPUs have a fair amount of level 3 cache, and the
most expensive ones might have a big level 4 cache, but I still think it
is a concern. Level 1 and 2 caches are small: 64KB/128KB.
