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SubjectRE: [PATCH 1/6] xenbus: prepare data structures and parameter for xenwatch multithreading
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> -----Original Message-----
> From: Dongli Zhang [mailto:dongli.zhang@oracle.com]
> Sent: 14 September 2018 08:34
> To: xen-devel@lists.xenproject.org; linux-kernel@vger.kernel.org
> Cc: boris.ostrovsky@oracle.com; jgross@suse.com; Paul Durrant
> <Paul.Durrant@citrix.com>; Wei Liu <wei.liu2@citrix.com>;
> konrad.wilk@oracle.com; Roger Pau Monne <roger.pau@citrix.com>;
> srinivas.eeda@oracle.com
> Subject: [PATCH 1/6] xenbus: prepare data structures and parameter for
> xenwatch multithreading
>
> This is the 1st patch of a (6-patch) patch set.
>
> This patch set of six patches introduces xenwatch multithreading (or
> multithreaded xenwatch, abbreviated as 'mtwatch') to dom0 kernel. In
> addition to the existing single xenwatch thread, each domU has its own
> kernel thread ([xen-mtwatch-<domid>]) to process its xenwatch event.
>

^ You need to put comments like this in a cover letter. Each patch needs to stand on its own merit and the comments should only relate to the context of that patch or a 'subsequent patch'.

> A kernel parameter 'xen_mtwatch' is introduced to control whether the
> feature is enabled or not during dom0 kernel boot. The feature is disabled
> by default if 'xen_mtwatch' is not set in grub.

Why is it disabled by default? Concerns about resource consumption?

> In addition, this patch
> also introduces the data structures to maintain the status of each per-
> domU
> xenwatch thread. The status of each xenwatch thread (except the default
> one) is maintained by a mtwatch domain.
>
> The feature is available only on dom0.

Whilst I can see it is intended for a backend domain, why limit it to dom0? What about driver domains?

>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
> ---
> Documentation/admin-guide/kernel-parameters.txt | 3 ++
> drivers/xen/xenbus/xenbus_xs.c | 31 ++++++++++++
> include/xen/xenbus.h | 65
> +++++++++++++++++++++++++
> 3 files changed, 99 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 64a3bf5..fc295ef 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4992,6 +4992,9 @@
> the unplug protocol
> never -- do not unplug even if version check succeeds
>
> + xen_mtwatch [KNL,XEN]
> + Enables the multithreaded xenwatch (mtwatch).
> +
> xen_nopvspin [X86,XEN]
> Disables the ticketlock slowpath using Xen PV
> optimizations.
> diff --git a/drivers/xen/xenbus/xenbus_xs.c
> b/drivers/xen/xenbus/xenbus_xs.c
> index 49a3874..3f137d2 100644
> --- a/drivers/xen/xenbus/xenbus_xs.c
> +++ b/drivers/xen/xenbus/xenbus_xs.c
> @@ -95,6 +95,19 @@ static pid_t xenwatch_pid;
> static DEFINE_MUTEX(xenwatch_mutex);
> static DECLARE_WAIT_QUEUE_HEAD(watch_events_waitq);
>
> +bool xen_mtwatch;
> +EXPORT_SYMBOL_GPL(xen_mtwatch);
> +
> +struct mtwatch_info *mtwatch_info;
> +
> +static bool param_xen_mtwatch;
> +static __init int xen_parse_mtwatch(char *arg)
> +{
> + param_xen_mtwatch = true;
> + return 0;
> +}
> +early_param("xen_mtwatch", xen_parse_mtwatch);
> +
> static void xs_suspend_enter(void)
> {
> spin_lock(&xs_state_lock);
> @@ -929,6 +942,24 @@ int xs_init(void)
> if (err)
> return err;
>
> + if (xen_initial_domain() && param_xen_mtwatch) {
> + int i;
> +
> + mtwatch_info = kmalloc(sizeof(*mtwatch_info), GFP_KERNEL);
> +
> + for (i = 0; i < MTWATCH_HASH_SIZE; i++)
> + INIT_HLIST_HEAD(&mtwatch_info->domain_hash[i]);
> + spin_lock_init(&mtwatch_info->domain_lock);
> + INIT_LIST_HEAD(&mtwatch_info->domain_list);
> +
> + spin_lock_init(&mtwatch_info->purge_lock);
> + INIT_LIST_HEAD(&mtwatch_info->purge_list);
> +
> + xen_mtwatch = true;
> +
> + pr_info("xenwatch multithreading is enabled\n");
> + }
> +
> task = kthread_run(xenwatch_thread, NULL, "xenwatch");
> if (IS_ERR(task))
> return PTR_ERR(task);
> diff --git a/include/xen/xenbus.h b/include/xen/xenbus.h
> index 869c816..e807114 100644
> --- a/include/xen/xenbus.h
> +++ b/include/xen/xenbus.h
> @@ -62,6 +62,13 @@ struct xenbus_watch
> /* Callback (executed in a process context with no locks held). */
> void (*callback)(struct xenbus_watch *,
> const char *path, const char *token);
> +
> + /* Callback to help calculate the domid the path belongs to */
> + domid_t (*get_domid)(struct xenbus_watch *watch,
> + const char *path, const char *token);
> +
> + /* The owner's domid if the watch is for a specific domain */
> + domid_t owner_id;
> };
>
>
> @@ -93,6 +100,7 @@ struct xenbus_device_id
> struct xenbus_driver {
> const char *name; /* defaults to ids[0].devicetype */
> const struct xenbus_device_id *ids;
> + bool use_mtwatch;
> int (*probe)(struct xenbus_device *dev,
> const struct xenbus_device_id *id);
> void (*otherend_changed)(struct xenbus_device *dev,
> @@ -233,4 +241,61 @@ extern const struct file_operations xen_xenbus_fops;
> extern struct xenstore_domain_interface *xen_store_interface;
> extern int xen_store_evtchn;
>
> +extern bool xen_mtwatch;
> +
> +#define MTWATCH_HASH_SIZE 256
> +#define MTWATCH_HASH(_id) ((int)(_id)&(MTWATCH_HASH_SIZE-1))
> +
> +struct mtwatch_info {
> + /*
> + * The mtwatch_domain is put on both a hash table and a list.
> + * domain_list is used to optimize xenbus_watch un-registration.
> + *
> + * The mtwatch_domain is removed from domain_hash (with state set
> + * to MTWATCH_DOMAIN_DOWN) when its refcnt is zero. However, it is
> + * left on domain_list until all events belong to such
> + * mtwatch_domain are processed in mtwatch_thread().
> + *
> + * While there may exist two mtwatch_domain with the same domid on
> + * domain_list simultaneously, all mtwatch_domain on hash_hash
> + * should have unique domid.
> + */
> + spinlock_t domain_lock;
> + struct hlist_head domain_hash[MTWATCH_HASH_SIZE];
> + struct list_head domain_list;
> +
> + /*
> + * When a per-domU

'per-frontend-domain' to be more descriptive?

Paul

> kthread is going to be destroyed, it is put
> + * on the purge_list, and will be flushed by purge_work later.
> + */
> + struct work_struct purge_work;
> + spinlock_t purge_lock;
> + struct list_head purge_list;
> +};
> +
> +enum mtwatch_domain_state {
> + MTWATCH_DOMAIN_UP = 1,
> + MTWATCH_DOMAIN_DOWN = 2,
> +};
> +
> +struct mtwatch_domain {
> + domid_t domid;
> + struct task_struct *task;
> + atomic_t refcnt;
> +
> + pid_t pid;
> + struct mutex domain_mutex;
> + struct rcu_head rcu;
> +
> + struct hlist_node hash_node;
> + struct list_head list_node;
> + struct list_head purge_node;
> +
> + wait_queue_head_t events_wq;
> +
> + spinlock_t events_lock;
> + struct list_head events;
> + enum mtwatch_domain_state state;
> +};
> +
> #endif /* _XEN_XENBUS_H */
> --
> 2.7.4

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