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Re: [Xen-devel] [PATCH RFC 01/49] xen/sched: call cpu_disable_scheduler() via cpu notifier
- To: Julien Grall <julien.grall@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 1 Apr 2019 11:40:02 +0200
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 01 Apr 2019 09:40:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 01/04/2019 11:21, Julien Grall wrote:
> Hi,
>
> On 3/29/19 3:08 PM, Juergen Gross wrote:
>> cpu_disable_scheduler() is being called from __cpu_disable() today.
>> There is no need to execute it on the cpu just being disabled, so use
>> the CPU_DEAD case of the cpu notifier chain. Moving the call out of
>> stop_machine() context is fine, as we just need to hold the domain RCU
>> lock and need the scheduler percpu data to be still allocated.
>>
>> Add another hook for CPU_DOWN_PREPARE to bail out early in case
>> cpu_disable_scheduler() would fail. This will avoid crashes in rare
>> cases for cpu hotplug or suspend.
>>
>> While at it remove a superfluous smp_mb() in the ARM __cpu_disable()
>> incarnation.
>
> This is not obvious why the smp_mb() is superfluous. Can you please
> provide more details on why this is not necessary?
cpumask_clear_cpu() should already have the needed semantics, no?
It is based on clear_bit() which is defined to be atomic.
Juergen
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