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

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Message-ID: <CACLfguX8vAMTz=vmnZtnqWSAawNps8UOboZ1DvZ-it6Gf8+4jQ@mail.gmail.com>
Date: Thu, 5 Jun 2025 15:34:56 +0800
From: Cindy Lu <lulu@...hat.com>
To: "Michael S. Tsirkin" <mst@...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 Sun, Jun 1, 2025 at 6:51 PM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> 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?
>
>
sure, will fix this
Thanks
cindy
> > ---
> >  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
>