Messages in this thread | | | Date | Wed, 6 Jun 2012 16:20:55 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi |
| |
On Wed, Jun 06, 2012 at 05:46:40PM +0200, Peter Zijlstra wrote: > On Wed, 2012-06-06 at 07:44 -0700, Paul E. McKenney wrote: > > > > I don't think the isolation means userspace while(1) applications is > > > interesting. Sure, some people do this, and we should dtrt for them, but > > > the far more interesting case is 'regular' applications that do use > > > system calls. > > > > OK, I will bite. What are the semantics/properties for your isolated set? > > The scheduler will not place tasks from outside the set in the set and > vice versa. Applications outside the set should not affect those in the > set, except there where there are shared resources across the set > boundary. > > So the example of 1 process with multiple threads, some inside some > outside have the obvious shared resource of the address space, hence TLB > invalidates etc. will come through.
So, for example, a way of nicely partitioning the system to allow multiple real-time applications to run without needing to do cross-partition global priority queuing of the real-time tasks. Cool!
> Now the kernel as a whole is also a shared resource, and this is where > it all gets tricky, since if something inside the set ends up doing a > memory allocation, it will have to participate in mm/ locks etc.
Yep.
> Same with RCU, if you cannot stay in an extended grace period for some > reason or other, you have to participate in the global RCU state > machinery.
Yep.
> But it should be so that if you don't do any of these things, you should > also not be affected by them. > > Now I realize this is a 'weak' model, but the 'strong' model proposed by > tglx would make it impossible to run anything but the while(1) stuff, > and that's of limited utility.
Thomas's strong model also supports a strong form of idle, as well as the while(1) stuff, both of which have their uses.
Thanx, Paul
| |