Subject: Re: [PATCH 3/3] vhost: apply cpumask and cgroup to vhost workers

From: "Michael S. Tsirkin" <[email-masked]>
Date: Tue, 1 Jun 2010 13:17:03 +0300

On Tue, Jun 01, 2010 at 11:35:15AM +0200, Tejun Heo wrote:
> Apply the cpumask and cgroup of the initializing task to the created
> vhost worker.
> 
> Based on Sridhar Samudrala's patch.  Li Zefan spotted a bug in error
> path (twice), fixed (twice).
> 
> Signed-off-by: Tejun Heo <[email-masked]>
> Cc: Michael S. Tsirkin <[email-masked]>
> Cc: Sridhar Samudrala <[email-masked]>
> Cc: Li Zefan <[email-masked]>

Something that I wanted to figure out - what happens if the
CPU mask limits us to a certain CPU that subsequently goes offline?
Will e.g. flush block forever or until that CPU comes back?
Also, does singlethreaded workqueue behave in the same way?

> ---
>  drivers/vhost/vhost.c |   34 ++++++++++++++++++++++++++++++----
>  1 file changed, 30 insertions(+), 4 deletions(-)
> 
> Index: work/drivers/vhost/vhost.c
> ===================================================================
> --- work.orig/drivers/vhost/vhost.c
> +++ work/drivers/vhost/vhost.c
> @@ -23,6 +23,7 @@
>  #include <linux/highmem.h>
>  #include <linux/slab.h>
>  #include <linux/kthread.h>
> +#include <linux/cgroup.h>
> 
>  #include <linux/net.h>
>  #include <linux/if_packet.h>
> @@ -187,11 +188,29 @@ long vhost_dev_init(struct vhost_dev *de
>  		    struct vhost_virtqueue *vqs, int nvqs)
>  {
>  	struct task_struct *worker;
> -	int i;
> +	cpumask_var_t mask;
> +	int i, ret = -ENOMEM;
> +
> +	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
> +		goto out_free_mask;
> 
>  	worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
> -	if (IS_ERR(worker))
> -		return PTR_ERR(worker);
> +	if (IS_ERR(worker)) {
> +		ret = PTR_ERR(worker);
> +		goto out_free_mask;
> +	}
> +
> +	ret = sched_getaffinity(current->pid, mask);
> +	if (ret)
> +		goto out_stop_worker;
> +
> +	ret = sched_setaffinity(worker->pid, mask);
> +	if (ret)
> +		goto out_stop_worker;
> +
> +	ret = cgroup_attach_task_current_cg(worker);
> +	if (ret)
> +		goto out_stop_worker;
> 
>  	dev->vqs = vqs;
>  	dev->nvqs = nvqs;
> @@ -214,7 +233,14 @@ long vhost_dev_init(struct vhost_dev *de
>  	}
> 
>  	wake_up_process(worker);	/* avoid contributing to loadavg */
> -	return 0;
> +	ret = 0;
> +	goto out_free_mask;
> +
> +out_stop_worker:
> +	kthread_stop(worker);
> +out_free_mask:
> +	free_cpumask_var(mask);
> +	return ret;
>  }
> 
>  /* Caller should have device mutex */