linux-kernel - Re: [PATCH RESEND v10 1/3] vhost: Add a new modparam to allow userspace select kthread

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Message-ID: <20250601064917-mutt-send-email-mst@kernel.org>
Date: Sun, 1 Jun 2025 06:51:32 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: jasowang@...hat.com, michael.christie@...cle.com, sgarzare@...hat.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH RESEND v10 1/3] vhost: Add a new modparam to allow
 userspace select kthread

On Sat, May 31, 2025 at 05:57:26PM +0800, Cindy Lu wrote:
> The vhost now uses vhost_task and workers as a child of the owner thread.
> While this aligns with containerization principles, it confuses some
> legacy userspace applications, therefore, we are reintroducing kthread
> API support.
> 
> Add a new module parameter to allow userspace to select behavior
> between using kthread and task.
> 
> By default, this parameter is set to true (task mode). This means the
> default behavior remains unchanged by this patch.
> 
> Signed-off-by: Cindy Lu <lulu@...hat.com>

So modparam is here but does nothing.
This should be the last patch in the series, or squashed with 3/3.

why is this inherit_owner but ioctl is fork_owner? is there
a difference? If not
can't the name be consistent with the ioctl?  vhost_fork_owner?


> ---
>  drivers/vhost/vhost.c |  5 +++++
>  drivers/vhost/vhost.h | 10 ++++++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 3a5ebb973dba..240ba78b1e3f 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -41,6 +41,10 @@ static int max_iotlb_entries = 2048;
>  module_param(max_iotlb_entries, int, 0444);
>  MODULE_PARM_DESC(max_iotlb_entries,
>  	"Maximum number of iotlb entries. (default: 2048)");
> +bool inherit_owner_default = true;
> +module_param(inherit_owner_default, bool, 0444);
> +MODULE_PARM_DESC(inherit_owner_default,
> +		 "Set task mode as the default(default: Y)");
>  
>  enum {
>  	VHOST_MEMORY_F_LOG = 0x1,
> @@ -552,6 +556,7 @@ void vhost_dev_init(struct vhost_dev *dev,
>  	dev->byte_weight = byte_weight;
>  	dev->use_worker = use_worker;
>  	dev->msg_handler = msg_handler;
> +	dev->inherit_owner = inherit_owner_default;
>  	init_waitqueue_head(&dev->wait);
>  	INIT_LIST_HEAD(&dev->read_list);
>  	INIT_LIST_HEAD(&dev->pending_list);
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index bb75a292d50c..c1ff4a92b925 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -176,6 +176,16 @@ struct vhost_dev {
>  	int byte_weight;
>  	struct xarray worker_xa;
>  	bool use_worker;
> +	/*
> +	 * If inherit_owner is true we use vhost_tasks to create
> +	 * the worker so all settings/limits like cgroups, NPROC,
> +	 * scheduler, etc are inherited from the owner. If false,
> +	 * we use kthreads and only attach to the same cgroups
> +	 * as the owner for compat with older kernels.
> +	 * here we use true as default value.
> +	 * The default value is set by modparam inherit_owner_default
> +	 */
> +	bool inherit_owner;
>  	int (*msg_handler)(struct vhost_dev *dev, u32 asid,
>  			   struct vhost_iotlb_msg *msg);
>  };
> -- 
> 2.45.0