[PATCH 2/2 net-next-2.6] net: QDISC_STATE_RUNNING dont need atomic bit ops

Eric Dumazet
2010-06-02T09:50:38Z

__QDISC_STATE_RUNNING is always changed while qdisc lock is held.

We can avoid two atomic operations in xmit path, if we move this bit in
a new __state container.

Location of this __state container is carefully chosen so that fast path
only dirties one qdisc cache line.

THROTTLED bit could later be moved into this __state location too, to
avoid dirtying first qdisc cache line.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
include/net/sch_generic.h | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index 9707dae..b3591e4 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -23,11 +23,17 @@ struct qdisc_rate_table {
};

enum qdisc_state_t {
- __QDISC_STATE_RUNNING,
__QDISC_STATE_SCHED,
__QDISC_STATE_DEACTIVATED,
};

+/*
+ * following bits are only changed while qdisc lock is held
+ */
+enum qdisc___state_t {
+ __QDISC___STATE_RUNNING,
+};
+
struct qdisc_size_table {
struct list_head list;
struct tc_sizespec szopts;
@@ -72,23 +78,24 @@ struct Qdisc {
unsigned long state;
struct sk_buff_head q;
struct gnet_stats_basic_packed bstats;
+ unsigned long __state;
struct gnet_stats_queue qstats;
struct rcu_head rcu_head;
};

static inline bool qdisc_is_running(struct Qdisc *qdisc)
{
- return test_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+ return test_bit(__QDISC___STATE_RUNNING, &qdisc->__state);
}

static inline bool qdisc_run_begin(struct Qdisc *qdisc)
{
- return !test_and_set_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+ return !__test_and_set_bit(__QDISC___STATE_RUNNING, &qdisc->__state);
}

static inline void qdisc_run_end(struct Qdisc *qdisc)
{
- clear_bit(__QDISC_STATE_RUNNING, &qdisc->state);
+ __clear_bit(__QDISC___STATE_RUNNING, &qdisc->__state);
}

struct Qdisc_class_ops {