Re: Boot time and 3 sec in warning_print

[Jan Beulich <jbeulich@xxxxxxxx>]

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.

> What was just an "annoyance" for boot can now completely wreck your 
> guests and system (not many software can tolerate large downtime).
> 
> So I think we either want to drop the 3s pause completely or allow the 
> user to decide whether he/she cares about it via a command line option.
> 
> I am leaning towards the former at the moment.

I'm afraid I'm -2 towards complete removal. I'm at least -1 towards
shortening of the pause, as already indicated.

Jan