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

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Message-Id: <1438849288-18112-4-git-send-email-dh.herrmann@gmail.com>
Date:	Thu,  6 Aug 2015 10:21:22 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Daniel Mack <daniel@...que.org>,
	Djalal Harouni <tixxdz@...ndz.org>,
	David Herrmann <dh.herrmann@...il.com>
Subject: [PATCH 3/9] kdbus: use separate counter for message IDs

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@...que.org>
Signed-off-by: David Herrmann <dh.herrmann@...il.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

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