Re: [Xen-devel] [PATCH 1/2] x86/VPMU: Disable VPMU when NMI watchdog is on

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 28/01/15 23:36, Boris Ostrovsky wrote:
> On 01/28/2015 05:41 PM, Andrew Cooper wrote:
>> On 28/01/2015 22:33, Boris Ostrovsky wrote:
>>> On 01/28/2015 04:49 PM, Andrew Cooper wrote:
>>>> On 28/01/2015 19:56, Boris Ostrovsky wrote:
>>>>> NMI watchdog sets APIC_LVTPC register to generate an NMI when PMU
>>>>> counter
>>>>> overflow occurs. This may be overwritten by VPMU code later,
>>>>> effectively
>>>>> turning off the watchdog.
>>>>>
>>>>> We should disable VPMU when NMI watchdog is running.
>>>>>
>>>>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>>>>
>>>> I completely agree with the aim, but this patch is clunky and you have
>>>> missed the case where neither 'watchdog' nor 'vpmu' is specified on
>>>> the
>>>> command line, but the booleans have been tweaked (which is the
>>>> XenServer
>>>> way of choosing defaults while keeping the length of the command line
>>>> down).
>>>
>>> You mean binary patching? Or does XenServer change those flags before
>>> compilation? Yes, I haven't thought about this.
>>
>> We patch the source before compiling.
>>
>> https://github.com/xenserver/xen-4.5.pg/blob/master/master/xen-tweak-cmdline-defaults.patch
>>
>
>
> How does this enable NMI watchdog? This patch sets watchdog_force but
> that alone doesn't enable anything. Or are there other changes that
> set opt_watchdog (which I was going to test as you suggested below).
>

It doesn't.  I was just citing a plausible example.  (For reasons which
temporally elude me, "watchdog" is still a set as a proper item on the
command line).  Apologies if I was not clear.

~Andrew



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