[libvirt] [PATCH v1 1/3] adding unplug_timeout QEMU conf

[Daniel Henrique Barboza]

On 8/30/19 5:24 AM, Daniel P. Berrangé wrote:
> On Mon, Aug 19, 2019 at 11:16:24AM +0200, Ján Tomko wrote:
>> On Sun, Aug 18, 2019 at 06:45:29PM -0300, Daniel Henrique Barboza wrote:
>>> For some architectures and setups, device removal can take
>>> longer than the default 5 seconds. This results in commands
>>> such as 'virsh setvcpus' to fire timeout messages even if
>>> the actual operation happened in the guest, causing confusion
>>> for the user.
>>>
>> The commit that introduced this error message:
>>     commit e3229f6e4461cd1721dc68a32e16ab1718ae716e
>>         qemu: hotplug: Add support for VCPU unplug
>>
>> specifically says that we treat this differently than regular device
>> detach:
>>
>>     As the new code is using device_del all the implications of using it
>>     are present. Contrary to the device deletion code, the vcpu deletion
>>     code fails if the unplug request is not executed in time.
>>
>> Technically, we already did execute the unplug request so we lie to the
>> user saying "operation failed".
>>
>> Maybe we can revisit the decision? [cc-ing pkrempa who added this]
>>
>>> This patch adds a new qemu.conf parameter called 'unplug_timeout'
>>> to handle these cases. If left unset, the current default
>>> timeout is used. To avoid user 'experimentation' with small
>>> timeouts, the current timeout is also the minimal value
>>> allowed.
>>>
>> The reason for this timeout is that we originally promised something
>> that we cannot deliver - a synchronous device detach API, while the
>> operation itself is asynchronous. I'm not a fan of exposing it and
>> making it configurable.
> I'm especially *not* a fan because the commit messages says this is
> a problem on certain architectures. Since we know what those arches
> are, we should use a larger timeout for those arches out of the box.
> Requiring admin to set a config param to fix the architectures is
> super unpleasant out of the box experiance.

Good point. I'll re-send the series changing the timeout for PowerPC
guests only. There's no need to impact all users for a problem that
so far only impacts PPC.


Thanks,


DHB

>
>
> Regards,
> Daniel