On Mon, 17 Apr 2006, Arnd Bergmann wrote: > Am Monday 17 April 2006 02:45 schrieb Steven Rostedt: > > > - does not work in real mode, so percpu data can't be used > > > inside exception handlers on some architectures. > > > > This is probably a big issue. I believe interrupt context in hrtimers > > uses per_cpu variables. > > If it's just about hrtimers, it should be harmless, since they > are run in softirq context. Even regular interrupt handlers are > always called with paging enabled, otherwise you could not > have them im modules. Ah, you're right. You said exceptions, I'm thinking interrupts. I was a little confused why it wouldn't work. > > > > - memory consumption is rather high when PAGE_SIZE is large > > > > That's also something that I'm trying to solve. To use the least amount > > of memory and still have the performance. > > > > Now, I've also thought about allocating per_cpu and when a module is > > loaded, reallocate more memory and copy it again. Use something like > > the kstopmachine to sync the system so that the CPUS don't update any > > per_cpu variables while this is happening, so that things can't get out > > of sync. > > I guess this breaks if someone holds a pointer to a per-cpu variable > while a module gets loaded. > Argh, good point, I didn't think about that. Hmm, this solution is looking harder and harder. Darn, I was really hoping this could be a little better in space savings and robustness. It's starting to seem clearer that Rusty's little hack, may be the best solution. If that's the case, I can at least take comfort in knowing that the time I spent on this is documented in LKML archives, and perhaps can keep others from spending the time too. That said, I haven't quite given up, and may spend a couple more sleepless nights pondering this. -- Steve
