2007/10/3, Alfred Perlstein <[EMAIL PROTECTED]>: > * Daniel Eischen <[EMAIL PROTECTED]> [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: > > /* assume single threaded process for now */ > static int is_critical; > > > > atomic_mutex_lock(); /* implies ++is_critical */ > ...do stuff... > atomic_mutex_unlock(); /* implies --is_critical */ > > We don't want two or more syscalls per lock operation. :)
Basically, preemption in kernelspace is handled by using the td_critnest counter which should work in this way: - critical_enter() bumps td_critnest - if preemption is required or an ipi arrives and the operation is signalled with the td_owepreempt flag and will be deferred. - once critical_exit() is called the counter is decreased. If necessary (checking for td_critnest and td_owepreempt) the preemptive operation happens instantanely. It is all very fast and highly scalable as scope of operation is entirely per-thread so it doesn't require any lock. I think maybe you should use a very similar scheme to this. Attilio -- Peace can only be achieved by understanding - A. Einstein _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
