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Date: Fri, 14 Aug 2009 13:49:07 +0530
From: Krishna Kumar <krkumar2@...ibm.com>
To: Jarek Poplawski <jarkao2@...il.com>
Cc: kaber@...sh.net, netdev@...r.kernel.org, davem@...emloft.net,
Krishna Kumar <krkumar2@...ibm.com>,
herbert@...dor.apana.org.au
Subject: Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap
Jarek Poplawski <jarkao2@...il.com> wrote on 08/13/2009 04:57:16 PM:
> > Sounds reasonable. To quantify that, I will test again for a longer
> > run and report the difference.
>
> Yes, more numbers would be appreciated.
I did a longer 7-hour testing of original code, public bitmap (the
code submitted earlier) and a private bitmap (patch below). Each
result line is aggregate of 5 iterations of individual 1, 2, 4, 8,
32 netperf sessions, each running for 55 seconds:
-------------------------------------------------------
IO Size Org Public Private
-------------------------------------------------------
4K 122571 126821 125913
16K 135715 135642 135530
128K 131324 131862 131668
256K 130060 130107 130378
-------------------------------------------------------
Total: 519670 524433 (0.92%) 523491 (0.74%)
-------------------------------------------------------
The difference between keeping the bitmap private and public is
not much.
> > The tests are on the latest tree which contains CAN_BYPASS. So a
> > single netperf process running this change will get no advantage
> > since this enqueue/dequeue never happens unless the NIC is slow.
> > But for multiple processes, it should help.
>
> I mean: since the previous patch saved ~2% on omitting enqueue/dequeue,
> and now enqueue/dequeue is ~2% faster, is it still worth to omit this?
I haven't tested the bitmap patch without the bypass code.
Theoretically I assume that patch should help as we still save
an enqueue/dequeue.
Thanks,
- KK
Signed-off-by: Krishna Kumar <krkumar2@...ibm.com>
---
net/sched/sch_generic.c | 70 ++++++++++++++++++++++++++------------
1 file changed, 48 insertions(+), 22 deletions(-)
diff -ruNp org/net/sched/sch_generic.c new2/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c 2009-08-07 12:05:43.000000000 +0530
+++ new2/net/sched/sch_generic.c 2009-08-14 12:48:37.000000000 +0530
@@ -406,18 +406,38 @@ static const u8 prio2band[TC_PRIO_MAX+1]
#define PFIFO_FAST_BANDS 3
-static inline struct sk_buff_head *prio2list(struct sk_buff *skb,
- struct Qdisc *qdisc)
+/*
+ * Private data for a pfifo_fast scheduler containing:
+ * - the three band queues
+ * - bitmap indicating which of the bands contain skbs.
+ */
+struct pfifo_fast_priv {
+ u32 bitmap;
+ struct sk_buff_head 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 bands.
+ * 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)
{
- struct sk_buff_head *list = qdisc_priv(qdisc);
- return list + prio2band[skb->priority & TC_PRIO_MAX];
+ return &priv->q[0] + band;
}
static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc* qdisc)
{
- struct sk_buff_head *list = prio2list(skb, qdisc);
+ int band = prio2band[skb->priority & TC_PRIO_MAX];
+ struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+ struct sk_buff_head *list = band2list(priv, band);
if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {
+ priv->bitmap |= (1 << band);
qdisc->q.qlen++;
return __qdisc_enqueue_tail(skb, qdisc, list);
}
@@ -427,14 +447,18 @@ static int pfifo_fast_enqueue(struct sk_
static struct sk_buff *pfifo_fast_dequeue(struct Qdisc* qdisc)
{
- int prio;
- struct sk_buff_head *list = qdisc_priv(qdisc);
+ struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+ int band = bitmap2band[priv->bitmap];
- for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
- if (!skb_queue_empty(list + prio)) {
- qdisc->q.qlen--;
- return __qdisc_dequeue_head(qdisc, list + prio);
- }
+ if (likely(band >= 0)) {
+ struct sk_buff_head *list = band2list(priv, band);
+ struct sk_buff *skb = __qdisc_dequeue_head(qdisc, list);
+
+ qdisc->q.qlen--;
+ if (skb_queue_empty(list))
+ priv->bitmap &= ~(1 << band);
+
+ return skb;
}
return NULL;
@@ -442,12 +466,13 @@ static struct sk_buff *pfifo_fast_dequeu
static struct sk_buff *pfifo_fast_peek(struct Qdisc* qdisc)
{
- int prio;
- struct sk_buff_head *list = qdisc_priv(qdisc);
+ struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
+ int band = bitmap2band[priv->bitmap];
+
+ if (band >= 0) {
+ struct sk_buff_head *list = band2list(priv, band);
- for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
- if (!skb_queue_empty(list + prio))
- return skb_peek(list + prio);
+ return skb_peek(list);
}
return NULL;
@@ -456,11 +481,12 @@ static struct sk_buff *pfifo_fast_peek(s
static void pfifo_fast_reset(struct Qdisc* qdisc)
{
int prio;
- struct sk_buff_head *list = qdisc_priv(qdisc);
+ struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
- __qdisc_reset_queue(qdisc, list + prio);
+ __qdisc_reset_queue(qdisc, band2list(priv, prio));
+ priv->bitmap = 0;
qdisc->qstats.backlog = 0;
qdisc->q.qlen = 0;
}
@@ -480,17 +506,17 @@ nla_put_failure:
static int pfifo_fast_init(struct Qdisc *qdisc, struct nlattr *opt)
{
int prio;
- struct sk_buff_head *list = qdisc_priv(qdisc);
+ struct pfifo_fast_priv *priv = qdisc_priv(qdisc);
for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
- skb_queue_head_init(list + prio);
+ skb_queue_head_init(band2list(priv, prio));
return 0;
}
static struct Qdisc_ops pfifo_fast_ops __read_mostly = {
.id = "pfifo_fast",
- .priv_size = PFIFO_FAST_BANDS * sizeof(struct sk_buff_head),
+ .priv_size = sizeof (struct pfifo_fast_priv),
.enqueue = pfifo_fast_enqueue,
.dequeue = pfifo_fast_dequeue,
.peek = pfifo_fast_peek,
--
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