Messages in this thread | | | Date | Sat, 09 Apr 2005 16:28:18 +1000 | From | Nick Piggin <> | Subject | Re: [patch] sched: unlocked context-switches |
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Ingo Molnar wrote: > * Luck, Tony <tony.luck@intel.com> wrote: > > >>>tested on x86, and all other arches should work as well, but if an >>>architecture has irqs-off assumptions in its switch_to() logic >>>it might break. (I havent found any but there may such assumptions.) >> >>The ia64_switch_to() code includes a section that can change a pinned >>MMU mapping (when the stack for the new process is in a different >>granule from the stack for the old process). [...] > > > thanks - updated patch below. Any other architectures that switch the > kernel stack in a nonatomic way? x86/x64 switches it atomically. >
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?
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?
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) ?
Thanks.
-- SUSE Labs, Novell Inc.
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