On Mon, 2007-09-24 at 18:54 +0100, Christoph Hellwig wrote: > As we already say in various messages the percpu counters in here > look rather fishy. I'd recomment to take a look at the per-cpu > superblock counters in XFS as they've been debugged quite well > now and could probably be lifted into a generic library for this > kind of think. The code is mostly in fs/xfs/xfs_mount.c can > can be spotted by beeing under #ifdef HAVE_PERCPU_SB. > > It also handles cases like hotplug cpu nicely that this code > seems to work around by always iterating over all possible cpus > which might not be nice on a dual core laptop with a distro kernel > that also has to support big iron.
I'll take a look at xfs to see what I can get out of it. There are basically two times when you have to do this for_each_possible_cpu() stuff: 1. when doing a r/w->r/o transition, which is rare, and certainly not a fast path 2. Where the per-cpu writer count underflows. This requires a _minimum_ of 1<<16 file opens (configurable) each of which is closed on a different cpu than it was opened on. Even if you were trying, I'm not sure you'd notice the overhead. -- Dave - 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/