Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap

Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap

[Krishna Kumar]

Hi Jarek,

Jarek Poplawski <jarkao2@gmail.com> wrote on 08/14/2009 04:31:27 PM:

> Alas, private or public, these values are lower on average than
> before, so I'm not sure the complexity (especially in reading) added
> by this patch is worth it. So, I can only say it looks formally OK,
> except the changelog and maybe 2 cosmetical suggestions below.

Maybe the different test parameters result in smaller improvements.
I agree with you - the first approach is very readable and probably
preferable, while the second introduces a new structure and more
complexity.

I am sending both these versions a last time, after fixing your
comments in case someone can help decide if one or the other is
better (sorry I forgot to run checkpatch couple of times, will try
to remember next time).

Thanks,

- KK

[PATCH v1] Speed-up pfifo_fast lookup using a public bitmap

[Krishna Kumar]

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---

 include/net/sch_generic.h |    1 
 net/sched/sch_generic.c   |   46 +++++++++++++++++++++++-------------
 2 files changed, 31 insertions(+), 16 deletions(-)

diff -ruNp org/include/net/sch_generic.h new/include/net/sch_generic.h
--- org/include/net/sch_generic.h	2009-08-07 12:05:43.000000000 +0530
+++ new/include/net/sch_generic.h	2009-08-13 16:55:32.000000000 +0530
@@ -72,6 +72,7 @@ struct Qdisc
 	 * For performance sake on SMP, we put highly modified fields at the end
 	 */
 	unsigned long		state;
+	u32			bitmap;
 	struct sk_buff_head	q;
 	struct gnet_stats_basic bstats;
 	struct gnet_stats_queue	qstats;
diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c	2009-08-07 12:05:43.000000000 +0530
+++ new/net/sched/sch_generic.c	2009-08-14 18:23:01.000000000 +0530
@@ -406,18 +406,28 @@ 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)
+/*
+ * 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 Qdisc *qdisc, int band)
 {
 	struct sk_buff_head *list = qdisc_priv(qdisc);
-	return list + prio2band[skb->priority & TC_PRIO_MAX];
+
+	return list + 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 sk_buff_head *list = band2list(qdisc, band);
 
 	if (skb_queue_len(list) < qdisc_dev(qdisc)->tx_queue_len) {
+		qdisc->bitmap |= (1 << band);
 		qdisc->q.qlen++;
 		return __qdisc_enqueue_tail(skb, qdisc, list);
 	}
@@ -427,14 +437,17 @@ 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);
+	int band = bitmap2band[qdisc->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 = qdisc_priv(qdisc);
+		struct sk_buff *skb = __qdisc_dequeue_head(qdisc, list + band);
+
+		qdisc->q.qlen--;
+		if (skb_queue_empty(list + band))
+			qdisc->bitmap &= ~(1 << band);
+
+		return skb;
 	}
 
 	return NULL;
@@ -442,12 +455,12 @@ 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);
+	int band = bitmap2band[qdisc->bitmap];
+
+	if (band >= 0) {
+		struct sk_buff_head *list = qdisc_priv(qdisc);
 
-	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++) {
-		if (!skb_queue_empty(list + prio))
-			return skb_peek(list + prio);
+		return skb_peek(list + band);
 	}
 
 	return NULL;
@@ -461,6 +474,7 @@ static void pfifo_fast_reset(struct Qdis
 	for (prio = 0; prio < PFIFO_FAST_BANDS; prio++)
 		__qdisc_reset_queue(qdisc, list + prio);
 
+	qdisc->bitmap = 0;
 	qdisc->qstats.backlog = 0;
 	qdisc->q.qlen = 0;
 }

[PATCH v2] Speed-up pfifo_fast lookup using a private bitmap

[Krishna Kumar]

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---

 net/sched/sch_generic.c |   70 ++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 22 deletions(-)

diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c	2009-08-07 12:05:43.000000000 +0530
+++ new/net/sched/sch_generic.c	2009-08-14 18:23:16.000000000 +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 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)
 {
-	struct sk_buff_head *list = qdisc_priv(qdisc);
-	return list + prio2band[skb->priority & TC_PRIO_MAX];
+	return priv->q + 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,

Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap

[Jarek Poplawski]

On Fri, Aug 14, 2009 at 06:54:58PM +0530, Krishna Kumar wrote:
> ďťżHi Jarek,
> 
> Jarek Poplawski <jarkao2@gmail.com> wrote on 08/14/2009 04:31:27 PM:
> 
> > Alas, private or public, these values are lower on average than
> > before, so I'm not sure the complexity (especially in reading) added
> > by this patch is worth it. So, I can only say it looks formally OK,
> > except the changelog and maybe 2 cosmetical suggestions below.
> 
> Maybe the different test parameters result in smaller improvements.
> I agree with you - the first approach is very readable and probably
> preferable, while the second introduces a new structure and more
> complexity.

Actually, I meant the complexity added by any of these versions. If
you declare: "This helps in faster lookup for a skb when there are no
high priority skbs.", there is a question if less than 1% is enough.

> I am sending both these versions a last time, after fixing your
> comments in case someone can help decide if one or the other is
> better (sorry I forgot to run checkpatch couple of times, will try
> to remember next time).

I definitely can't see a reason to make this variable public, and
prefer the private (v2) version (which still lacks a changelog, btw).

Thanks,
Jarek P.

Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap

[David Miller]

From: Jarek Poplawski <jarkao2@gmail.com>
Date: Fri, 14 Aug 2009 23:36:43 +0200

> I definitely can't see a reason to make this variable public, and
> prefer the private (v2) version (which still lacks a changelog, btw).

I'm fine with patch v2, but yes it needs to be properly submitted
with a real changelog before I can apply it :-)

Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap

[Krishna Kumar2]

Sorry about the delay, I am sick with the flu for the last few days.
I will send the patch tomorrow.

thanks,

- KK

David Miller <davem@davemloft.net> wrote on 08/18/2009 07:33:43 AM:

> David Miller <davem@davemloft.net>
> 08/18/2009 07:33 AM
>
> To
>
> jarkao2@gmail.com
>
> cc
>
> Krishna Kumar2/India/IBM@IBMIN, kaber@trash.net, netdev@vger.kernel.org,
> herbert@gondor.apana.org.au
>
> Subject
>
> Re: [PATCH] Speed-up pfifo_fast lookup using a bitmap
>
> From: Jarek Poplawski <jarkao2@gmail.com>
> Date: Fri, 14 Aug 2009 23:36:43 +0200
>
> > I definitely can't see a reason to make this variable public, and
> > prefer the private (v2) version (which still lacks a changelog, btw).
>
> I'm fine with patch v2, but yes it needs to be properly submitted
> with a real changelog before I can apply it :-)

[PATCH v2] Speed-up pfifo_fast lookup using a private bitmap

[Krishna Kumar]

From: Krishna Kumar <krkumar2@in.ibm.com>

Maintain a per-qdisc bitmap for pfifo_fast giving  availability
of skbs for each band. This allows faster lookup for a skb when
there are no high priority skbs. Also, it helps in (rare) cases
when there are no skbs on the list, where an immediate lookup is
faster than iterating through the three bands.

Changelog v1 -> v2

1. Moved the bitmap from Qdisc to the private area of pfifo_fast
2. pfifo_fast_reset sets bitmap to zero
3. Undo a line-wrap in initializing a variable
4. Fixed some comments
5. Readability and checkpatch fixes

Thanks,

- KK

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---

 net/sched/sch_generic.c |   70 ++++++++++++++++++++++++++------------
 1 file changed, 48 insertions(+), 22 deletions(-)

diff -ruNp org/net/sched/sch_generic.c new/net/sched/sch_generic.c
--- org/net/sched/sch_generic.c	2009-08-07 12:05:43.000000000 +0530
+++ new/net/sched/sch_generic.c	2009-08-14 18:23:16.000000000 +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:
+ * 	- queues for the three band
+ * 	- 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 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)
 {
-	struct sk_buff_head *list = qdisc_priv(qdisc);
-	return list + prio2band[skb->priority & TC_PRIO_MAX];
+	return priv->q + 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,

Re: [PATCH v2] Speed-up pfifo_fast lookup using a private bitmap

[David Miller]

From: Krishna Kumar <krkumar2@in.ibm.com>
Date: Wed, 19 Aug 2009 13:25:59 +0530

> From: Krishna Kumar <krkumar2@in.ibm.com>
> 
> Maintain a per-qdisc bitmap for pfifo_fast giving  availability
> of skbs for each band. This allows faster lookup for a skb when
> there are no high priority skbs. Also, it helps in (rare) cases
> when there are no skbs on the list, where an immediate lookup is
> faster than iterating through the three bands.
> 
> Changelog v1 -> v2
> 
> 1. Moved the bitmap from Qdisc to the private area of pfifo_fast
> 2. pfifo_fast_reset sets bitmap to zero
> 3. Undo a line-wrap in initializing a variable
> 4. Fixed some comments
> 5. Readability and checkpatch fixes
> 
> Thanks,
> 
> - KK
> 
> Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>

Applied, thanks.