On Fri, Jul 06, 2007 at 04:12:10PM +1000, Nick Piggin wrote: > Mathieu Desnoyers wrote: > >Thread Migration Preemption > > > >This patch adds the ability to protect critical sections from migration to > >another CPU without disabling preemption. > > > >This will be useful to minimize the amount of preemption disabling for the > >-rt > >patch. It will help leveraging improvements brought by the local_t types in > >asm/local.h (see Documentation/local_ops.txt). Note that the updates done > >to > >variables protected by migration_disable must be either atomic or > >protected from > >concurrent updates done by other threads. > > > >Typical use: > > > >migration_disable(); > >local_inc(&__get_cpu_var(&my_local_t_var)); > >migration_enable(); > > > >Which will increment the variable atomically wrt the local CPU. > > > >Comments (such as how to integrate this in the already almost full > >preempt_count) are welcome. > > This seems like way too much stuff to add just for this type of thing. Why > not just disable and reenable preempt? Surely local_inc is not going to take > so long that disabling preemption matters.
I like this patch a lot. Even if we don't add the underlying mechanism right now, adding migration_disable as an alias for preempt_disable will much better document quite a number of the users. > The task struct is not something we should just be carefree putting crap > into because it is seemingly free :( Sadly, it is free at the moment. We can only fit 3 task_structs in an order-1 SLAB, with lots of slop. -- Mathematics is the supreme nostalgia of our time. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/