[Linux-ia64] Re: O(1) MQ scheduler J9 patch for IA64

[David Mosberger <davidm@hpl.hp.com>]

  Erich> I had to add a function smp_call_function_nowait which sends
  Erich> an IPI and returns immediately in order to get rid of a
  Erich> IA64-specific race condition when the mmu_context wraps
  Erich> around. Now it makes a very stable and fast impression,
  Erich> interactive work is even possible while doing a "hackbench
  Erich> 55" and ping flooding the machine... Tested on 2 CPU BigSur,
  Erich> 4 CPU LION, 16 CPU AzusA.

Hmmh, I'm a bit worried that this is a fragile solution.  It would
break if there ever was a scenario where a task migrated from one CPU
to another while the target CPU has interrupts disabled.  I do not
think this can happen with Ingo's current scheduler but I'd prefer a
more robust solution.

A somewhat cheesy solution might be to have a per-CPU flag that
indicates whether a CPU should flush its TLB before switching to the
next task.  We could check for this in activate_mm().  Do you want to
try this?

	--david