Re: Boot time and 3 sec in warning_print

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.02.2021 11:50, Julien Grall wrote:
> Hi Jan,
> 
> On 15/02/2021 10:41, Jan Beulich wrote:
>> On 15.02.2021 11:35, Julien Grall wrote:
>>> On 15/02/2021 08:38, Jan Beulich wrote:
>>>> On 15.02.2021 09:13, Jürgen Groß wrote:
>>>>> On 15.02.21 08:37, Anders Törnqvist wrote:
>>>>>> I would like to shorten the boot time in our system if possible.
>>>>>>
>>>>>> In xen/common/warning.c there is warning_print() which contains a 3
>>>>>> seconds loop that calls  process_pending_softirqs().
>>>>>>
>>>>>> What would the potential problems be if that loop is radically shortened?
>>>>>
>>>>> A user might not notice the warning(s) printed.
>>>>>
>>>>> But I can see your point. I think adding a boot option for setting
>>>>> another timeout value (e.g. 0) would do the job without compromising
>>>>> the default case.
>>>>
>>>> I don't think I agree - the solution to this is to eliminate the
>>>> reason leading to the warning.
>>>   >
>>>> The delay is intentionally this way
>>>> to annoy the admin and force them to take measures.
>>> Given they are warning, an admin may have assessed them and considered
>>> there is no remediation necessary.
>>>
>>> We encountered the same problem with LiveUpdate. If you happen to have a
>>> warning (e.g. sync_console for debugging), then you are adding 3s in
>>> your downtime (this can more than double-up the actual one).
>>
>> One very explicitly should not run with sync_console in production.
> 
> I knew it would be misinterpreted ;). I agree that sync_console must not 
> be used in production.
> 
> I gave the example of sync_console because this is something impacting 
> debugging of LiveUpdate. If you have a console issue and need to add 
> sync_console, then you may end up to wreck completely your platform when 
> LiveUpdating.
> 
> Without the 3s delay, then you have a chance to LiveUpdate and figure 
> out the problem.

I'm afraid I don't see how LU comes into the picture here: We're
talking about a boot time delay. The delay doesn't recur at any
point at runtime.

Jan