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Re: [Xen-devel] [PATCH 4/6] xen: don't free percpu areas during suspend
- To: Jan Beulich <JBeulich@xxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Thu, 28 Mar 2019 09:35:39 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wei.liu2@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 28 Mar 2019 08:35:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 28/03/2019 09:04, Jan Beulich wrote:
>>>> On 28.03.19 at 08:53, <jgross@xxxxxxxx> wrote:
>> On 28/03/2019 08:46, Jan Beulich wrote:
>>>>>> On 18.03.19 at 14:11, <jgross@xxxxxxxx> wrote:
>>>> Instead of freeing percpu areas during suspend and allocating them
>>>> again when resuming keep them. Only free an area in case a cpu didn't
>>>> come up again when resuming.
>>>
>>> There's another aspect here which needs at least mentioning:
>>> Right now, CPUs coming back up have their per-CPU data
>>> cleared. Not doing so may indeed be an improvement in
>>> some cases (like statistics collected), but may also get in the
>>> way in other cases.
>>
>> I have checked the respective cpu notifier hooks and I think this is no
>> problem. I hope I didn't overlook something.
>
> Is checking the hooks sufficient? I'd rather expect we need to
> check all per-CPU data objects.
Why? The main concern would be a hook not doing its job due to some
data not being zeroed.
In case there is a dependency somewhere else I'd rather expect subtle
negative effects with today's solution as suddenly percpu data will
be zero after suspend/resume without a component having been involved
with suspending.
Sure, there could be negative effects with my series, but I'd asset the
chances lower as without my series. Suspend/resume tends to be not
tested very often, it seems. I guess I'm the only one having it tried
recently (it was broken for 3 months at least before my patch repairing
an issue with IOMMU).
Juergen
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