linux-kernel - Re: [PATCH v8 1/8] vhost: Add a new parameter in vhost

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Message-ID: <74u5ppfmuf4gwjup3eotpnd6bulocerdk4l54qvykfcnesf6hm@udabnuiw2v6y>
Date: Tue, 1 Apr 2025 15:30:17 +0200
From: Stefano Garzarella <sgarzare@...hat.com>
To: Cindy Lu <lulu@...hat.com>
Cc: jasowang@...hat.com, mst@...hat.com, michael.christie@...cle.com, 
	linux-kernel@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH v8 1/8] vhost: Add a new parameter in vhost_dev to allow
 user select kthread

On Fri, Mar 28, 2025 at 06:02:45PM +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

nit: missing space "principles,it"

>userspace app, Therefore, we are reintroducing kthread API support.

nit: "userspace app, Therefore" -> "userspace app. Therefore"

>
>Introduce a new parameter to enable users to choose between
>kthread and task mode.

I would explain that by default this is true, and so we are not changing 
the behavior with this patch.

>
>Signed-off-by: Cindy Lu <lulu@...hat.com>
>---
> drivers/vhost/vhost.c | 1 +
> drivers/vhost/vhost.h | 9 +++++++++
> 2 files changed, 10 insertions(+)

Anyway, the patch LGTM with or without the commit tweaks:

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

>
>diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>index 63612faeab72..250dc43f1786 100644
>--- a/drivers/vhost/vhost.c
>+++ b/drivers/vhost/vhost.c
>@@ -552,6 +552,7 @@ 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 = true;
> 	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..19bb94922a0e 100644
>--- a/drivers/vhost/vhost.h
>+++ b/drivers/vhost/vhost.h
>@@ -176,6 +176,15 @@ 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
>+	 */
>+	bool inherit_owner;
> 	int (*msg_handler)(struct vhost_dev *dev, u32 asid,
> 			   struct vhost_iotlb_msg *msg);
> };
>-- 
>2.45.0
>