On Mon, 23 Feb 2015, Peter Zijlstra wrote: > In any case, having had a second look I think I might have some ideas: > > - bL_switcher_enable() -- enables the whole switcher thing and > disables half the cpus with hot-un-plug, creates a mapping etc.. > > - bL_switcher_disable() -- disabled the whole switcher thing and > gives us back all our cpus with hot-plug. > > When the switcher is enabled; we switch by this magic cpu_suspend() call > that saves the entire cpu state and allows you to restore it on another > cpu. > > You muck about with the tick; you disable it before cpu_suspend() and > re-enable it after on the target cpu. You further reprogram the > interrupt routing from the old to the new cpu. > > But that appears to be it, no more.
Exact. > I suppose the tick is special because its the only per-cpu device? Right. > The reported function that fails: bL_switcher_restore_cpus() is called > in the error paths of the former and the main path in the latter to make > the 'stolen' cpus re-appear. > > The patch in question somehow makes that go boom. > > > Now what all do you need to do to make it go boom? Just enable/disable > the switcher once and it'll explode? Or does it need to do actual > switches while it is enabled? It gets automatically enabled during boot. Then several switches are performed while user space is brought up. If I manually disable it via /sys then it goes boom. > The place where it explodes is a bit surprising, it thinks hrtimers are > not enabled even though its calling into hrtimer code on that cpu... > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
