[RFC PATCH 09/12] net: sched: pfifo_fast use alf_queue

John Fastabend
2015-12-30T17:54:39Z

This converts the pfifo_fast qdisc to use the alf_queue enqueue
and dequeue routines then sets the NOLOCK bit.

This also removes the logic used to pick the next band to dequeue
from and instead just checks each alf_queue for packets from
top priority to lowest. This might need to be a bit more clever
but seems to work for now.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
---
net/sched/sch_generic.c | 120 +++++++++++++++++++++++++----------------------
1 file changed, 65 insertions(+), 55 deletions(-)

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index be5d63a..480cf63 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -26,6 +26,7 @@
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/if_vlan.h>
+#include <linux/alf_queue.h>
#include <net/sch_generic.h>
#include <net/pkt_sched.h>
#include <net/dst.h>
@@ -467,87 +468,80 @@ static const u8 prio2band[TC_PRIO_MAX + 1] = {

/*
* Private data for a pfifo_fast scheduler containing:
- * - queues for the three band
- * - bitmap indicating which of the bands contain skbs
+ * - rings for the priority bands
*/
struct pfifo_fast_priv {
- u32 bitmap;
- struct sk_buff_head q[PFIFO_FAST_BANDS];
+ struct alf_queue *q[PFIFO_FAST_BANDS];
};

-/*
- * Convert a bitmap to the first band number where an skb is queued, where:
- * bitmap=0 means there are no skbs on any band.
- * bitmap=1 means there is an skb on band 0.
- * bitmap=7 means there are skbs on all 3 bands, etc.
- */
-static const int bitmap2band[] = {-1, 0, 1, 0, 2, 0, 1, 0};
-
-static inline struct sk_buff_head *band2list(struct pfifo_fast_priv *priv,
- int band)
+static inline struct alf_queue *band2list(struct pfifo_fast_priv *priv,
+ int band)
{
- return priv->q + band;
+ return priv->q[band];
}

static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc)
{
- if (skb_queue_len(&qdisc->q) < qdisc_dev(qdisc)->tx_queue_len) {
- int band = prio2band[skb->priority & TC_PRIO_MAX];
- struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
- struct sk_buff_head *list = band2list(priv, band);
-
- priv->bitmap |= (1 << band);
- qdisc->q.qlen++;
- return __qdisc_enqueue_tail(skb, qdisc, list);
- }
-
- return qdisc_drop(skb, qdisc);
-}
-
-static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
-{
+ int band = prio2band[skb->priority & TC_PRIO_MAX];
struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
- int band = bitmap2band[priv->bitmap];
+ struct alf_queue *q = band2list(priv, band);
+ int n;

- if (likely(band >= 0)) {
- struct sk_buff_head *list = band2list(priv, band);
- struct sk_buff *skb = __qdisc_dequeue_head(qdisc, list);
+ if (!q) {
+ WARN_ON(1);
+ return qdisc_drop(skb, qdisc);
+ }

- qdisc->q.qlen--;
- if (skb_queue_empty(list))
- priv->bitmap &= ~(1 << band);
+ n = alf_mp_enqueue(q, &skb, 1);

- return skb;
+ /* If queue is overrun fall through to drop */
+ if (n) {
+ qdisc_qstats_cpu_qlen_inc(qdisc);
+ qdisc_qstats_cpu_backlog_inc(qdisc, skb);
+ return NET_XMIT_SUCCESS;
}

- return NULL;
+ return qdisc_drop_cpu(skb, qdisc);
}

-static struct sk_buff *pfifo_fast_peek(struct Qdisc *qdisc)
+static struct sk_buff *pfifo_fast_dequeue(struct Qdisc *qdisc)
{
struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
- int band = bitmap2band[priv->bitmap];
+ struct sk_buff *skb = NULL;
+ int band;
+
+ for (band = 0; band < PFIFO_FAST_BANDS && !skb; band++) {
+ struct alf_queue *q = band2list(priv, band);

- if (band >= 0) {
- struct sk_buff_head *list = band2list(priv, band);
+ if (alf_queue_empty(q))
+ continue;

- return skb_peek(list);
+ alf_mc_dequeue(q, &skb, 1);
}

- return NULL;
+ if (likely(skb)) {
+ qdisc_qstats_cpu_backlog_dec(qdisc, skb);
+ qdisc_bstats_cpu_update(qdisc, skb);
+ qdisc_qstats_cpu_qlen_dec(qdisc);
+ }
+
+ return skb;
}

static void pfifo_fast_reset(struct Qdisc *qdisc)
{
- int prio;
+ int i, band;
struct pfifo_fast_priv *priv = qdisc_priv(qdisc);

- for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
- __qdisc_reset_queue(qdisc, band2list(priv, prio));
+ for (band = 0; band < PFIFO_FAST_BANDS; band++)
+ alf_queue_flush(band2list(priv, band));

- priv->bitmap = 0;
- qdisc->qstats.backlog = 0;
- qdisc->q.qlen = 0;
+ for_each_possible_cpu(i) {
+ struct gnet_stats_queue *q = per_cpu_ptr(qdisc->cpu_qstats, i);
+
+ q->backlog = 0;
+ q->qlen = 0;
+ }
}

static int pfifo_fast_dump(struct Qdisc *qdisc, struct sk_buff *skb)
@@ -565,14 +559,30 @@ nla_put_failure:

static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt)
{
- int prio;
+ unsigned int qlen = qdisc_dev(qdisc)->tx_queue_len;
struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+ int prio;
+
+ /* guard against zero length rings */
+ if (!qlen)
+ return -EINVAL;
+
+ for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
+ unsigned int size = roundup_pow_of_two(qlen);
+ struct alf_queue *q;

- for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
- __skb_queue_head_init(band2list(priv, prio));
+ q = alf_queue_alloc(size, GFP_KERNEL);
+ if (IS_ERR_OR_NULL(q))
+ return -ENOMEM;
+
+ priv->q[prio] = q;
+ }

/* Can by-pass the queue discipline */
qdisc->flags |= TCQ_F_CAN_BYPASS;
+ qdisc->flags |= TCQ_F_NOLOCK;
+ qdisc->flags |= TCQ_F_CPUSTATS;
+
return 0;
}

@@ -581,7 +591,7 @@ struct Qdisc_ops pfifo_fast_ops __read_mostly = {
.priv_size = sizeof(struct pfifo_fast_priv),
.enqueue = pfifo_fast_enqueue,
.dequeue = pfifo_fast_dequeue,
- .peek = pfifo_fast_peek,
+ .peek = qdisc_peek_dequeued,
.init = pfifo_fast_init,
.reset = pfifo_fast_reset,
.dump = pfifo_fast_dump,