Messages in this thread | | | Date | Sat, 9 Apr 2005 08:55:07 +0200 | From | Ingo Molnar <> | Subject | Re: [patch] sched: unlocked context-switches |
| |
* Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> Well that does look like a pretty good cleanup. It certainly is the > final step in freeing complex architecture switching code from > entanglement with scheduler internal locking, and unifies the locking > scheme. > > I did propose doing unconditionally unlocked switches a while back > when my patch first popped up - you were against it then, but I guess > you've had second thoughts?
the reordering of switch_to() and the switch_mm()-related logic was that made it really worthwile and clean. I.e. we pick a task atomically, we switch stacks, and then we switch the MM. Note that this setup still leaves the possibility open to move the stack-switching back under the irq-disabled section in a natural way.
> It does add an extra couple of stores to on_cpu, and a wmb() for > architectures that didn't previously need the unlocked switches. And > ia64 needs the extra interrupt disable / enable. Probably worth it?
it also removes extra stores to rq->prev_mm and other stores. I havent measured any degradation on x86.
If the irq disable/enable becomes widespread i'll do another patch to push the irq-enabling into switch_to() so the arch can do the stack-switch first and then enable interrupts and do the rest - but i didnt want to complicate things unnecessarily for now.
> Minor style request: I like that you're accessing ->on_cpu through > functions so the !SMP case doesn't clutter the code with ifdefs... but > can you do set_task_on_cpu(p) and clear_task_on_cpu(p) ?
yeah, i thought about these two variants and went for set_task_on_cpu() so that it's less encapsulated (it's really just a conditional assignment) and that it parallels set_task_cpu() use. But no strong feelings either way. Anyway, lets try what we have now, i'll do the rest in deltas.
Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |