Messages in this thread | | | Date | Thu, 1 Jan 2009 02:48:26 +0100 | From | Andi Kleen <> | Subject | Re: [PATCH 0/2] pdflush fix and enhancement |
| |
On Wed, Dec 31, 2008 at 09:08:26AM -0700, Peter W. Morreale wrote: > On Wed, 2008-12-31 at 14:27 +0100, Andi Kleen wrote: > > > I say most because the assumption would be that we will be successful in > > > creating the new thread. Not that bad an assumption I think. Besides, > > > > And that the memory read is not reordered (rmb()). > > > > At the risk of showing my b*tt here... I'm not very clear on memory > barriers, is this necessary even inside a critical region? (recall > we're protected by the spin lock).
You're right the implied barriers in the spinlock are probably enough. Never mind.
> If so, does the barrier go after the > read, or before? (Thanks for not laughing, however grins are allowed)
Before.
BTW on x86 it's a nop either way, but not on all other architectures.
> > > > > > Ok it probably needs some kind of feedback mechanism. > > > > Actually, I tend to think we need an entirely different approach to > flushing, please see my post to David Chinner which outlines some > thoughts. Basically a flushing heuristic that takes into account the > characteristics of the various block devices.
Ideally discovered at runtime (e.g. by watching queue lengths/service times etc.) though. Otherwise the kernel would need to have knowledge about the properties of all kinds of devices.
-Andi -- ak@linux.intel.com
| |