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SubjectRe: [PATCH v4 2/2] misc: Add a mechanism to detect stalls on guest vCPUs
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On 4/29/22 23:18, Greg Kroah-Hartman wrote:
> On Fri, Apr 29, 2022 at 09:51:51AM -0700, Guenter Roeck wrote:
>> On 4/29/22 01:48, Greg Kroah-Hartman wrote:
>>> On Fri, Apr 29, 2022 at 08:30:33AM +0000, Sebastian Ene wrote:
>>>> This driver creates per-cpu hrtimers which are required to do the
>>>> periodic 'pet' operation. On a conventional watchdog-core driver, the
>>>> userspace is responsible for delivering the 'pet' events by writing to
>>>> the particular /dev/watchdogN node. In this case we require a strong
>>>> thread affinity to be able to account for lost time on a per vCPU.
>>>>
>>>> This part of the driver is the 'frontend' which is reponsible for
>>>> delivering the periodic 'pet' events, configuring the virtual peripheral
>>>> and listening for cpu hotplug events. The other part of the driver
>>>> handles the peripheral emulation and this part accounts for lost time by
>>>> looking at the /proc/{}/task/{}/stat entries and is located here:
>>>> https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3548817
>>>>
>>>> Signed-off-by: Sebastian Ene <sebastianene@google.com>
>>>> ---
>>>> drivers/misc/Kconfig | 12 +++
>>>> drivers/misc/Makefile | 1 +
>>>> drivers/misc/vm-watchdog.c | 206 +++++++++++++++++++++++++++++++++++++
>>>> 3 files changed, 219 insertions(+)
>>>> create mode 100644 drivers/misc/vm-watchdog.c
>>>>
>>>> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
>>>> index 2b9572a6d114..26c3a99e269c 100644
>>>> --- a/drivers/misc/Kconfig
>>>> +++ b/drivers/misc/Kconfig
>>>> @@ -493,6 +493,18 @@ config OPEN_DICE
>>>> If unsure, say N.
>>>> +config VM_WATCHDOG
>>>> + tristate "Virtual Machine Watchdog"
>>>> + select LOCKUP_DETECTOR
>>>> + help
>>>> + Detect CPU locks on the virtual machine. This driver relies on the
>>>> + hrtimers which are CPU-binded to do the 'pet' operation. When a vCPU
>>>> + has to do a 'pet', it exits the guest through MMIO write and the
>>>> + backend driver takes into account the lost ticks for this particular
>>>> + CPU.
>>>> + To compile this driver as a module, choose M here: the
>>>> + module will be called vm-wdt.
>>>
>>> You forgot to name the module properly here based on the Makefile change
>>> you made.
>>>
>>> And again, as this is called a "watchdog", it seems crazy that it is not
>>> in drivers/watchdog/
>>>
>>
>> I disagree. It is not a watchdog driver in the traditional sense (it does
>> not use, want to use, or need to use the watchdog driver API or ABI).
>> Its functionality is similar to the functionality of kernel/watchdog.c,
>> which doesn't belong into drivers/watchdog either.
>
> Ah, ok, that makes more sense, the user/kernel api is not the same.
> Someone should put that in the changelog next time :)
>

Renaming it to "VCPU stall detector" or similar should fix the confusion.

Guenter

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