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Date: Sat, 23 Mar 2013 20:42:37 +0000
From: Eric Wong <normalperson@...t.net>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Lai Jiangshan <laijs@...fujitsu.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Stephen Hemminger <shemminger@...tta.com>,
Davide Libenzi <davidel@...ilserver.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH v3] wfcqueue: functions for local append and enqueue
Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> * Eric Wong (normalperson@...t.net) wrote:
> > /*
> > + * ___wfcq_append: append one local queue to another local queue
> > + *
> __wfcq_append() and ___wfcq_append() are meant to be private to
> wfcqueue.h. Therefore, the comment above should be removed, since it is
> not part of the API.
>
> I notice that I should have used ___wfcq_append() for the original
> append function for consistency (other private helpers in this header
> are prefixed with ___).
>
> So maybe we should rename __wfcq_append to ___wfcq_append (making it
> clear that it is a private helper), and introduce your helper as
> ___wfcq_append_local() (I don't care about having "local" in there since
> it is not part of the exposed API).
Thanks for the explanation, I've squashed that renames into my patch
below and removed the comment.
> > +/*
> > + * __wfcq_enqueue: enqueue a node into a local queue
>
> The concept of "local queue" is not clearly defined.
>
> Perhaps it would be clearer to state:
>
> * __wfcq_enqueue: enqueue a node into a queue, requiring mutual exclusion.
Sounds good to me. Updated patch below:
-------------------------------8<-----------------------------
From: Eric Wong <normalperson@...t.net>
Date: Sat, 23 Mar 2013 19:07:26 +0000
Subject: [PATCH] wfcqueue: functions for local append and enqueue
With level-triggered epoll, append/enqueue operations to the
local/locked queues increase performance by avoiding unnecessary atomic
operations and barriers. These are necessary to avoid performance
regressions when looping through ep_send_events and appending many items
to a local queue where the caller already manages mutual exclusion.
Changes since v1 and v2:
* Function renaming and documentation updates
* rename the existing private __wfcq_append to ___wfcq_append
Signed-off-by: Eric Wong <normalperson@...t.net>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Stephen Hemminger <shemminger@...tta.com>
Cc: Davide Libenzi <davidel@...ilserver.org>
---
include/linux/wfcqueue.h | 56 +++++++++++++++++++++++++++++++++++++++---------
1 file changed, 46 insertions(+), 10 deletions(-)
diff --git a/include/linux/wfcqueue.h b/include/linux/wfcqueue.h
index 9464a0c..a452ab9 100644
--- a/include/linux/wfcqueue.h
+++ b/include/linux/wfcqueue.h
@@ -55,14 +55,16 @@
* [4] __wfcq_splice (source queue)
* [5] __wfcq_first
* [6] __wfcq_next
+ * [7] __wfcq_enqueue
*
- * [1] [2] [3] [4] [5] [6]
- * [1] - - - - - -
- * [2] - - - - - -
- * [3] - - X X X X
- * [4] - - X - X X
- * [5] - - X X - -
- * [6] - - X X - -
+ * [1] [2] [3] [4] [5] [6] [7]
+ * [1] - - - - - - X
+ * [2] - - - - - - X
+ * [3] - - X X X X X
+ * [4] - - X - X X X
+ * [5] - - X X - - X
+ * [6] - - X X - - X
+ * [7] X X X X X X X
*
* Besides locking, mutual exclusion of dequeue, splice and iteration
* can be ensured by performing all of those operations from a single
@@ -147,7 +149,7 @@ static inline bool wfcq_empty(struct wfcq_head *head,
&& CMM_LOAD_SHARED(tail->p) == &head->node;
}
-static inline bool __wfcq_append(struct wfcq_head *head,
+static inline bool ___wfcq_append(struct wfcq_head *head,
struct wfcq_tail *tail,
struct wfcq_node *new_head,
struct wfcq_node *new_tail)
@@ -201,7 +203,41 @@ static inline bool wfcq_enqueue(struct wfcq_head *head,
struct wfcq_tail *tail,
struct wfcq_node *new_tail)
{
- return __wfcq_append(head, tail, new_tail, new_tail);
+ return ___wfcq_append(head, tail, new_tail, new_tail);
+}
+
+static inline bool ___wfcq_append_local(struct wfcq_head *head,
+ struct wfcq_tail *tail,
+ struct wfcq_node *new_head,
+ struct wfcq_node *new_tail)
+{
+ struct wfcq_node *old_tail;
+
+ old_tail = tail->p;
+ tail->p = new_tail;
+ old_tail->next = new_head;
+
+ /*
+ * Return false if queue was empty prior to adding the node,
+ * else return true.
+ */
+ return old_tail != &head->node;
+}
+
+/*
+ * __wfcq_enqueue: enqueue a node into a queue, requiring mutual exclusion.
+ *
+ * No memory barriers are issued. Mutual exclusion is the responsibility
+ * of the caller.
+ *
+ * Returns false if the queue was empty prior to adding the node.
+ * Returns true otherwise.
+ */
+static inline bool __wfcq_enqueue(struct wfcq_head *head,
+ struct wfcq_tail *tail,
+ struct wfcq_node *new_tail)
+{
+ return ___wfcq_append_local(head, tail, new_tail, new_tail);
}
/*
@@ -398,7 +434,7 @@ static inline enum wfcq_ret __wfcq_splice(
* Append the spliced content of src_q into dest_q. Does not
* require mutual exclusion on dest_q (wait-free).
*/
- if (__wfcq_append(dest_q_head, dest_q_tail, head, tail))
+ if (___wfcq_append(dest_q_head, dest_q_tail, head, tail))
return WFCQ_RET_DEST_NON_EMPTY;
else
return WFCQ_RET_DEST_EMPTY;
--
1.8.2.rc3.2.geae6cf5
--
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