[patch] ARM: smpboot: Enable interrupts after marking CPU online/active
Frank Rowand
frank.rowand at am.sony.com
Tue Sep 13 21:10:38 EDT 2011
On 09/13/11 10:53, Russell King - ARM Linux wrote:
> On Tue, Sep 13, 2011 at 07:22:16PM +0200, Vincent Guittot wrote:
>> The assumption done in the 1st patch that smp_store_cpu_info can be
>> delayed is no more true. The smp_store_cpu_info is now also used to
>> store the cpu topology information
>> (https://lkml.org/lkml/2011/7/5/209). This must be done before calling
>> sched_init_smp, which will use this information for building
>> sched_domain.
>> If we move set_cpu_online before smp_store_cpu_info, sched_init_smp
>> can be called before having called smp_store_cpu_info on all cpus.
>
> Right. We hold off returning from cpu_up() by watching for the upcoming
> CPU setting its online bit.
>
> The bug which Thomas' patch introduces is to move the setting of that
> before we've finished bringing the CPU up - specifically, allowing the
> requesting CPU to continue while the brought-up CPU is still calibrating
> loops_per_jiffy, and before it's stored that information and setup the
> scheduler domain information.
>
> The other issue is that moving the marking of the CPU online in the
> way Thomas has means that we then invite the delivery of IPIs to the
> CPU which is still in the process of coming up. Whether that's an
> issue depends on what the IPIs are.
>
> So, we must have the setting of CPU online _after_ we've setup the
> scheduler domain information etc - so the following is a strict
> ordering:
>
> 1. calibrate_delay()
> 2. smp_store_cpu_info()
> 3. set_cpu_online()
>
> Now, the question is do we need interrupts enabled to setup timers
> via percpu_timer_setup() and calibrate delay. Can we move enabling
> interrupts after smp_store_cpu_info(). IOW, instead of moving the
> setting of cpu online before all this, can we move notify_cpu_starting()
> and the enabling of _both_ interrupts after smp_store_cpu_info()...
> No idea at the moment.
Modified the patch from Thomas to move enabling interrupts after
smp_store_cpu_info(), as suggested by Russell.
Tested on RealView (3.0.1, 3.0.1-rt11), Panda (3.0.0, 3.0.3-rt12).
The calibrate_delay() is platform specific, so be aware that there are
more platforms that I did not test.
Note that these kernel versions do not have the store_cpu_topology()
that Vincent pointed out.
Signed-off-by: Frank Rowand <frank.rowand at am.sony.com>
---
arch/arm/kernel/smp.c | 14 7 + 7 - 0 !
1 file changed, 7 insertions(+), 7 deletions(-)
Index: b/arch/arm/kernel/smp.c
===================================================================
--- a/arch/arm/kernel/smp.c
+++ b/arch/arm/kernel/smp.c
@@ -303,13 +303,6 @@ asmlinkage void __cpuinit secondary_star
platform_secondary_init(cpu);
/*
- * Enable local interrupts.
- */
- notify_cpu_starting(cpu);
- local_irq_enable();
- local_fiq_enable();
-
- /*
* Setup the percpu timer for this CPU.
*/
percpu_timer_setup();
@@ -328,6 +321,13 @@ asmlinkage void __cpuinit secondary_star
cpu_relax();
/*
+ * Enable local interrupts.
+ */
+ notify_cpu_starting(cpu);
+ local_irq_enable();
+ local_fiq_enable();
+
+ /*
* OK, it's off to the idle thread for us
*/
cpu_idle();
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