Re: [uml-devel] 'current' and such (was: [PATCH] use set_current instead of 'current = x')

[Jeff D. <jd...@ka...>]

bu...@gn... said:
> I think people on l-k mostly agreed that pipes are the way to go for
> lightweight user-level semaphores.  I'm not sure why they didn't think
> much of SysV sems,  

Hmmm, if someone could dig up a reference, that would be good.

> Are you sure that these scheduler oddities are happening right now?

I think so, but I have no idea how often.  My data is old, though.  The very
first context switcher I wrote for UML had a bug which caused a hang if this
scheduler oddity happened.  And it happened often enough that UML hung reliably
on boot.

> I think if read/write on pipe gives bad scheduler behavior, that is a
> scheduler bug (pipelines have pretty much the same model). 

And I think it's possible that the scheduler runs the reader immediately
after the write on purpose.  I have a hazy recollection that this was done
so that the written data would still be in L1 cache when the reader ran.

				Jeff