On Thu, Nov 22, 2007 at 12:10:29PM -0600, Matt Mackall wrote: > On Thu, Nov 22, 2007 at 09:31:59PM +1100, David Chinner wrote: > [...] > > > In other words, I/O priority is per-spindle and not per-filesystem and > > > thus this change has consequences that leak outside the filesystem in > > > question. That's bad. > > > > This has nothing to do with this patch - it's a problem with sharing > > a single resource in a RT system between two non-deterministic > > constructs. e.g. I can put two ext3 filesystems on the one spindle, > > run two completely independent RT workloads on the different > > filesystems and have one workload DOS the other due to differences > > in priority at the spindle. > > Sure. And it's up to the RT system designer not to do something stupid > like that. The problem is that your patch potentially promotes a > non-RT I/O activity to an RT one without regard to the rest of the > system.
So this: http://marc.info/?l=linux-kernel&m=119247074517414&w=2 shouldn't be allowed, either? (rt kjournald for ext3) > Perfectly understood. And that's fine. A system designer is allowed to > shoot himself in the foot. Ok. I'll point anyone that complains at you, Matt ;) > I don't think there's any fundamental reason the I/O subsystem or > filesystems can't be taught to handle priority inversion, which is > much more acceptable and general fix. See my reply to Andi. > If I've got XFS on filesystems A and B on the same spindle (or volume > group?) and my real RT I/O takes place only on B, then I want log > flushing to happen in RT on B. But -never on A-. If I can do this with > a tunable, I'm perfectly happy. No, not another mount option. I'm just going to drop this one for now... Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group - 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/