Messages in this thread | | | Date | Thu, 6 Dec 2001 12:10:04 -0800 | From | Larry McVoy <> | Subject | Re: SMP/cc Cluster description |
| |
On Thu, Dec 06, 2001 at 09:10:51PM +0100, Daniel Phillips wrote: > On December 6, 2001 08:53 pm, Larry McVoy wrote: > > On Thu, Dec 06, 2001 at 08:42:05PM +0100, Daniel Phillips wrote: > > > On December 6, 2001 09:02 am, Larry McVoy wrote: > > > > On Wed, Dec 05, 2001 at 11:56:17PM -0800, David S. Miller wrote: > > > > > These lockless algorithms, instructions like CAS, DCAS, "infinite > > > > > consensus number", it's all crap. You have to seperate out the access > > > > > areas amongst different cpus so they don't collide, and none of these > > > > > mechanisms do that. > > > > > > > > Err, Dave, that's *exactly* the point of the ccCluster stuff. You get > > > > all that seperation for every data structure for free. Think about > > > > it a bit. Aren't you going to feel a little bit stupid if you do all > > > > this work, one object at a time, and someone can come along and do the > > > > whole OS in one swoop? Yeah, I'm spouting crap, it isn't that easy, > > > > but it is much easier than the route you are taking. > > > > > > What I don't get after looking at your material, is how you intend to do the > > > locking. Sharing a mmap across OS instances is fine, but how do processes on > > > the two different OS's avoid stepping on each other when they access the same > > > file? > > > > Exactly the same way they would if they were two processes on a traditional > > SMP OS. > > They'd use locks internal to the VFS and fs, plus Posix-style locks and > assorted other userland serializers, which don't come for free. As davem > said, you'll have to present a coherent namespace, that's just one of the > annoying details. So far you haven't said much about how such things are > going to be handled.
Huh? Of course not, they'd use mutexes in a mmap-ed file, which uses the hardware's coherency. No locks in the vfs or fs, that's all done in the mmap/page fault path for sure, but once the data is mapped you aren't dealing with the file system at all. -- --- Larry McVoy lm at bitmover.com http://www.bitmover.com/lm - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |