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Re: [Xen-devel] [PATCH 3/6] xen: add new cpu notifier action CPU_RESUME_FAILED
- To: Dario Faggioli <dfaggioli@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Mon, 25 Mar 2019 13:29:30 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Mon, 25 Mar 2019 12:29:41 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 25/03/2019 13:21, Dario Faggioli wrote:
> On Mon, 2019-03-18 at 14:11 +0100, Juergen Gross wrote:
>> --- a/xen/include/xen/cpu.h
>> +++ b/xen/include/xen/cpu.h
>> @@ -32,23 +32,25 @@ void register_cpu_notifier(struct notifier_block
>> *nb);
>> * (a) A CPU is going down; or (b) CPU_UP_CANCELED
>> */
>> /* CPU_UP_PREPARE: Preparing to bring CPU online. */
>> -#define CPU_UP_PREPARE (0x0001 | NOTIFY_FORWARD)
>> +#define CPU_UP_PREPARE (0x0001 | NOTIFY_FORWARD)
>>
> In the comment block before these definitions, there's this:
>
> * Possible event sequences for a given CPU:
> * CPU_UP_PREPARE -> CPU_UP_CANCELLED -- failed CPU up
> * CPU_UP_PREPARE -> CPU_STARTING -> CPU_ONLINE -- successful CPU up
> * CPU_DOWN_PREPARE -> CPU_DOWN_FAILED -- failed CPU down
> * CPU_DOWN_PREPARE -> CPU_DYING -> CPU_DEAD -- successful CPU down
>
> Shouldn't we add a line for this new hook? Something, IIUIC, like:
>
> CPU_UP_PREPARE -> CPU_UP_CANCELLED -> CPU_RESUME_FAILED --CPU not resuming
Fine with me.
>
> With this, FWIW,
>
> Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>
>
> One more (minor) thing...
>
>> /* CPU_REMOVE: CPU was removed. */
>> -#define CPU_REMOVE (0x0009 | NOTIFY_REVERSE)
>> +#define CPU_REMOVE (0x0009 | NOTIFY_REVERSE)
>> +/* CPU_RESUME_FAILED: CPU failed to come up in resume, all other CPUs up. */
>> +#define CPU_RESUME_FAILED (0x000a | NOTIFY_REVERSE)
>>
> ... technically, when we're dealing with CPU_RESUME_FAILED on one CPU,
> we don't know if _all_ others really went up, so I think I'd remove
> what follows the ','.
The point is that for the CPU_RESUME_FAILED case we can be sure that no
cpu will come up due to resume just a little bit later. So we can test
for e.g. a cpupool suddenly having no more cpus available. This is in
contrast to CPU_UP_CANCELLED being signalled just after the one cpu
failing to come up, but before the next cpu is triggered to come up.
Juergen
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