Hi,
On Dec 11, 2016, at 10:55 AM, Christopher Collins
<[email protected]> wrote:
On Sun, Dec 11, 2016 at 10:11:44AM -0800, will sanfilippo wrote:
Personally, I keep wanting to try and have the OS start up right
away.
I wonder if this could solve the problem that Sterling raised (no
default event queue during sysinit). The control flow in main()
might
look like this:
1. Start OS
2. Create and designate default event queue.
3. sysinit()
I think it would be nice if we could avoid adding another
initialization
stage.
+1
There are definitely “issues” with this:
a) We do not want to waste idle task stack.
b) When tasks are started they would start running right away. This
might cause issues where a task does something to a piece of memory
that another task initializes, but since that other task has not
initialized it yet…
b) can be avoided by locking the scheduler until initializations are
finished.
a) is problematic :-) I think someone brought this up before, but I
wonder if it is worth the effort to do something “a bit crazy”
like
the following: the idle task uses “the heap” during
intialization.
Once initializations are over (or at some point that we determine),
the idle task stack is made smaller and the “top” of the heap is
set
to the end of the idle task stack. For example, idle task stack is
at
0x20008000 and is of size 1K bytes; the bottom of the heap is at
0x20007000; the top of the heap is at 0x20007C00 (in my
nomenclature,
heap allocations start from the bottom). At some point, the top of
the
heap is moved to 0x20007F80.
Yeah, maybe a bit crazy… :-)
I don't think that's too crazy. It would be great if we could just
malloc() a temporary stack, and then free it when initialization
completes. I guess the worry is that this will cause heap
fragmentation?
I’m not crazy about malloc()’ing this space. Especially since
system init (where we’d use this memory) is where people malloc()
their memory pools, and so you have 1K of space that could potentially
affect memory exhaustion. Maybe its an awful idea… but why not let
people specify the startup task stack, and we can guarantee that this
task gets deleted before the rest of the tasks/system runs. That way,
you can just choose one of your task’s stacks that is sufficiently
large, and use that for startup stack.
Sterling
