[PATCH 3/9] kdbus: use separate counter for message IDs

David Herrmann
2015-08-06T08:22:05Z

For each kdbus domain, we maintain an ID-counter to guarantee unique IDs
across all objects. We also used to use it for message IDs. However, this
requires touching a shared cacheline on each message transaction, even
though we never guaranteed global ordering across buses, anyway.

Introduce a separate counter which is used solely for message IDs.
Semantics stay the same, but it no longer relates to IDs across buses.

Reviewed-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
ipc/kdbus/bus.h | 2 ++
ipc/kdbus/message.c | 2 +-
2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/ipc/kdbus/bus.h b/ipc/kdbus/bus.h
index 238986e..8c2acae 100644
--- a/ipc/kdbus/bus.h
+++ b/ipc/kdbus/bus.h
@@ -44,6 +44,7 @@ struct kdbus_user;
* @domain: Domain of this bus
* @creator: Creator of the bus
* @creator_meta: Meta information about the bus creator
+ * @last_message_id: Last used message id
* @policy_db: Policy database for this bus
* @name_registry: Name registry of this bus
* @conn_rwlock: Read/Write lock for all lists of child connections
@@ -67,6 +68,7 @@ struct kdbus_bus {
struct kdbus_meta_proc *creator_meta;

/* protected by own locks */
+ atomic64_t last_message_id;
struct kdbus_policy_db policy_db;
struct kdbus_name_registry *name_registry;

diff --git a/ipc/kdbus/message.c b/ipc/kdbus/message.c
index 432dba4..ae565cd 100644
--- a/ipc/kdbus/message.c
+++ b/ipc/kdbus/message.c
@@ -671,7 +671,7 @@ static struct kdbus_staging *kdbus_staging_new(struct kdbus_bus *bus,
if (!staging)
return ERR_PTR(-ENOMEM);

- staging->msg_seqnum = atomic64_inc_return(&bus->domain->last_id);
+ staging->msg_seqnum = atomic64_inc_return(&bus->last_message_id);
staging->n_parts = 0; /* we reserve n_parts, but don't enforce them */
staging->parts = (void *)(staging + 1);

--
2.5.0