* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > I have this dim memory that ARM has done it that way for a long time > because it's so expensive to do a "real" cli/sti. > > And I think -rt does it for other reasons. It's just more flexible. -rt doesnt wrap cli/sti anymore: spin_lock_irq*() doesnt disable irq flags on -rt, thus the amount of real irqs-off sections is very small and reviewable. But nevertheless an incarnation of the code survived and is upstream already, in the form of TRACE_IRQFLAGS lockdep code ;) This implements a soft hardirq flag _today_: all that would be needed is for Xen to define raw_local_irq_disable() as a NOP, and to use the current->hardirqs_enabled as 'soft IRQ-off flag'. Note that ->hardirqs_enabled is self-maintained, i.e. it's not just a stupid shadow of the hardirq flag, it's an independently maintained flag that does not rely on the existence of the hard flag. [ this code even has its own debugging code, so out-of-sync-flags, double-off and double-on is detected and complained about. So all the hard stuff has already been done as part of lockdep, and it's even long-term maintainable because under a native lockdep kernel we check the soft flag against the hard flag. ] so i think a soft cli/sti flag support should be merged/unified with the trace_hardirqs_on()/trace_hardirqs_off() code. Ingo _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
