On Mon, 24 Sep 2007 12:28:11 -0700 Dave Hansen <[EMAIL PROTECTED]> wrote:
> 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. And at include/linux/percpu_counter.h, please. > 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. > Sounds like what you're doing is more akin to the local_t-based module refcounting. `grep local_ kernel/module.c'. That code should be converted from NR_CPUS to for_each_possible_cpu().. - 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/