Critical Sections for userland.
Alfred Perlstein
alfred at freebsd.org
Tue Oct 2 20:09:44 PDT 2007
* Daniel Eischen <deischen at freebsd.org> [071002 20:02] wrote:
> On Tue, 2 Oct 2007, Alfred Perlstein wrote:
>
> >* Daniel Eischen <deischen at freebsd.org> [071002 19:46] wrote:
> >>On Tue, 2 Oct 2007, Alfred Perlstein wrote:
> >>
> >>>Hi guys, we need critical sections for userland here.
> >>>
> >>>This is basically to avoid a process being switched out while holding
> >>>a user level spinlock.
> >>
> >>Setting the scheduling class to real-time and using SCHED_FIFO
> >>and adjusting the thread priority around the lock doesn't work?
> >
> >Too heavy weight, we want to basically have this sort of code
> >in userland:
>
> Well, yeah, but are you _really_ sure that you aren't just
> running something that should be real-time and have priority
> over other applications? SCHED_FIFO means you will run until
> you relinquish the CPU (you can only do this as root). If
> all your threads are well behaved, would this work? Have
> you tried it?
No, because it wouldn't work. How do we know when to let go
of the cpu? In my system, the kernel tells you without polling.
>
> Are you trying to prevent switching out of the thread
> amongst other threads of the same application, or all
> threads in the system?
All threads on that CPU.
It's basically, almost like a "soft spl" for userland.
Right?
--
- Alfred Perlstein
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