linux-kernel - Re: [PATCH v11 2/2] misc: Add a mechanism to detect stalls on guest vCPUs

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Date:   Fri, 8 Jul 2022 15:47:23 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sebastian Ene <sebastianene@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        maz@...nel.org, will@...nel.org, vdonnefort@...gle.com,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v11 2/2] misc: Add a mechanism to detect stalls on guest
 vCPUs

On Fri, Jul 08, 2022 at 11:23:45AM +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 is
> an emulated MMIO device which is part of the KVM virtual machine
> monitor and this part accounts for lost time by looking at the
> /proc/{}/task/{}/stat entries.
> 
> Reviewed-by: Will Deacon <will@...nel.org>
> Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> ---
>  drivers/misc/Kconfig               |  14 ++
>  drivers/misc/Makefile              |   1 +
>  drivers/misc/vcpu_stall_detector.c | 223 +++++++++++++++++++++++++++++
>  3 files changed, 238 insertions(+)
>  create mode 100644 drivers/misc/vcpu_stall_detector.c
> 
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 41d2bb0ae23a..d5b7610459f7 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -483,6 +483,20 @@ config OPEN_DICE
>  
>  	  If unsure, say N.
>  
> +config VCPU_STALL_DETECTOR
> +	tristate "Guest vCPU stall detector"
> +	select LOCKUP_DETECTOR

This should be a "depends on", not a select, right?  This got enabled on
my build when I didn't want it to, and trying to track down why it was
enabled would be a pain for people.

thanks,

greg k-h