Re: [Xen-devel] [PATCH] x86/nmi: lower initial watchdog frequency to avoid boot hangs

[Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>]

On 06/02/18 16:07, Jan Beulich wrote:
>>>> On 05.02.18 at 22:18, <igor.druzhinin@xxxxxxxxxx> wrote:
>> --- a/xen/arch/x86/nmi.c
>> +++ b/xen/arch/x86/nmi.c
>> @@ -34,7 +34,8 @@
>>  #include <asm/apic.h>
>>  
>>  unsigned int nmi_watchdog = NMI_NONE;
>> -static unsigned int nmi_hz = HZ;
>> +/* initial watchdog frequency - shouldn't be too high to avoid boot hangs */
>> +static unsigned int nmi_hz = HZ / 10;
> 
> For one - the comment should explain what "too high" means.
> Further - what if on another system 10Hz is still too high? I also hope
> you realize that you slow down boot a little for everyone just
> because of this one machine model. Can the lower frequency perhaps
> be set via DMI quirk, or otherwise obtain a command line override
> (perhaps something like "watchdog=probe:10Hz")?
>

I can improve the comment message.
Why does this change slow down anything while I'm lowering the frequency
- not making it higher? The alternative approach would be to reshuffle
the code and take the reason before programming the next interrupt as
suggested before. In that case the actual frequency would be adjusted
naturally I think.

Igor

> Jan
> 

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