Re: [PATCH 03/18] xen/pvcalls: initialize the module and register the xenbus backend

[Juergen Gross]

On 15/05/17 22:35, Stefano Stabellini wrote:
> The pvcalls backend has one ioworker per cpu: the ioworkers are
> implemented as a cpu bound workqueue, and will deal with the actual
> socket and data ring reads/writes.
> 
> ioworkers are global: we only have one set for all the frontends. They
> process requests on their wqs list in order, once they are done with a
> request, they'll remove it from the list. A spinlock is used for
> protecting the list. Each ioworker is bound to a different cpu to
> maximize throughput.
> 
> Signed-off-by: Stefano Stabellini <stefano@xxxxxxxxxxx>
> CC: boris.ostrovsky@xxxxxxxxxx
> CC: jgross@xxxxxxxx
> ---
>  drivers/xen/pvcalls-back.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 64 insertions(+)
> 
> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> index 2dbf7d8..46a889a 100644
> --- a/drivers/xen/pvcalls-back.c
> +++ b/drivers/xen/pvcalls-back.c
> @@ -25,6 +25,26 @@
>  #include <xen/xenbus.h>
>  #include <xen/interface/io/pvcalls.h>
>  
> +struct pvcalls_ioworker {
> +	struct work_struct register_work;
> +	atomic_t io;
> +	struct list_head wqs;
> +	spinlock_t lock;
> +	int num;
> +};
> +
> +struct pvcalls_back_global {
> +	struct pvcalls_ioworker *ioworkers;
> +	int nr_ioworkers;
> +	struct workqueue_struct *wq;
> +	struct list_head privs;
> +	struct rw_semaphore privs_lock;
> +} pvcalls_back_global;
> +
> +static void pvcalls_back_ioworker(struct work_struct *work)
> +{
> +}
> +
>  static int pvcalls_back_probe(struct xenbus_device *dev,
>  			      const struct xenbus_device_id *id)
>  {
> @@ -59,3 +79,47 @@ static int pvcalls_back_uevent(struct xenbus_device *xdev,
>  	.uevent = pvcalls_back_uevent,
>  	.otherend_changed = pvcalls_back_changed,
>  };
> +
> +static int __init pvcalls_back_init(void)
> +{
> +	int ret, i, cpu;
> +
> +	if (!xen_domain())
> +		return -ENODEV;
> +
> +	ret = xenbus_register_backend(&pvcalls_back_driver);
> +	if (ret < 0)
> +		return ret;
> +
> +	init_rwsem(&pvcalls_back_global.privs_lock);
> +	INIT_LIST_HEAD(&pvcalls_back_global.privs);
> +	pvcalls_back_global.wq = alloc_workqueue("pvcalls_io", 0, 0);
> +	if (!pvcalls_back_global.wq)
> +		goto error;
> +	pvcalls_back_global.nr_ioworkers = num_online_cpus();

Really? Recently I cam across a system with 640 dom0 cpus. I don't think
we want 640 workers initialized when loading the backend module. I'd
prefer one or a few workers per connected frontend.

> +	pvcalls_back_global.ioworkers = kzalloc(
> +		sizeof(*pvcalls_back_global.ioworkers) *
> +		pvcalls_back_global.nr_ioworkers, GFP_KERNEL);

kcalloc()?

> +	if (!pvcalls_back_global.ioworkers)
> +		goto error;
> +	i = 0;
> +	for_each_online_cpu(cpu) {
> +		pvcalls_back_global.ioworkers[i].num = i;
> +		atomic_set(&pvcalls_back_global.ioworkers[i].io, 1);
> +		spin_lock_init(&pvcalls_back_global.ioworkers[i].lock);
> +		INIT_LIST_HEAD(&pvcalls_back_global.ioworkers[i].wqs);
> +		INIT_WORK(&pvcalls_back_global.ioworkers[i].register_work,
> +			pvcalls_back_ioworker);
> +		i++;
> +	}
> +	return 0;
> +
> +error:
> +	if (pvcalls_back_global.wq)
> +		destroy_workqueue(pvcalls_back_global.wq);
> +	xenbus_unregister_driver(&pvcalls_back_driver);
> +	kfree(pvcalls_back_global.ioworkers);
> +	memset(&pvcalls_back_global, 0, sizeof(pvcalls_back_global));
> +	return -ENOMEM;
> +}
> +module_init(pvcalls_back_init);
> 

Juergen