Messages in this thread Patch in this message | | | Date | Fri, 30 Sep 2011 09:09:40 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: [PATCH RFC 0/8] jump-label: allow early jump_label_enable() |
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On 09/30/2011 08:28 AM, Steven Rostedt wrote: > On Thu, 2011-09-29 at 21:40 -0700, Jeremy Fitzhardinge wrote: >> On 09/29/2011 05:52 PM, Steven Rostedt wrote: >>> On Thu, 2011-09-29 at 16:26 -0700, Jeremy Fitzhardinge wrote: >>>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> >>>> >>>> One big question which arises is whether the _early() function is >>>> necessary at all. All the stop_machine/mutex/etc stuff that >>>> arch_jump_label_transform() ends up doing is redundant pre-SMP, but it >>>> shouldn't hurt. Maybe we can just drop the _early function? It works >>>> on x86, at least, because jump_label_enable() works, which uses the full >>>> form. And dropping it would reduce this to a very much smaller series. >>> It does slow down the boot process, which is not a good thing when >>> everyone is pushing for the fastest restarts. >> Would it really though? stop_machine() doesn't do very much when there >> are no other cpus. >> >> Not that I measured or anything, but there was no obvious big lag at boot. > Just bringing up the point, but without measurements, its all hand > waving. It may not be a big deal, and simpler code is always better if > it doesn't harm anything else.
I think the simplest thing is to make stop_machine() well-defined in a pre-smp environment, where it just directly calls the callback:
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index ba5070c..b6ad9b3 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -485,6 +485,11 @@ int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus) .num_threads = num_online_cpus(), .active_cpus = cpus }; + if (smdata.num_threads == 1) { + (*fn)(data); + return 0; + } + /* Set the initial state and stop all online cpus. */ set_state(&smdata, STOPMACHINE_PREPARE); return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata); so that its guaranteed safe to use at any point.
J
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