* [PATCH] pkt_sched: fix bandwidth's accuracy of software device with htb
@ 2013-07-31 2:39 Yang Yingliang
2013-07-31 3:08 ` Eric Dumazet
0 siblings, 1 reply; 2+ messages in thread
From: Yang Yingliang @ 2013-07-31 2:39 UTC (permalink / raw)
To: Jamal Hadi Salim, David S. Miller, netdev
When we set bandwidth on the software devices with htb,
it's not precise.
With htb, sch->limit is set from devices TX queue's
length that is not 0. Because software devices TX
queue is 0, sch->limit is set to default value 1.
Because the length of skb_buff queue is bigger than
sch->limit whose value is 1, some packets are dropped.
This leads to software devices can't make full use of
the bandwidth and influence the accuracy.
To fix this issue, set the default value of sch->limit
to 1000 that is the value of eth device's tx_queueu_len.
Example:
tc qdisc add dev bond0 root handle 1: htb default 1
tc class add dev bond0 parent 1:0 classid 1:1 htb rate 1Gbit ceil 1Gbit
iperf -c host -t 30 -i 10
With old sch->limit:
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 579 MBytes 486 Mbits/sec
[ 3] 10.0-20.0 sec 604 MBytes 507 Mbits/sec
[ 3] 20.0-30.0 sec 551 MBytes 462 Mbits/sec
[ 3] 0.0-30.0 sec 1.69 GBytes 485 Mbits/sec
With new sch->limit:
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-10.0 sec 1.11 GBytes 955 Mbits/sec
[ 3] 10.0-20.0 sec 1.11 GBytes 955 Mbits/sec
[ 3] 20.0-30.0 sec 1.11 GBytes 955 Mbits/sec
[ 3] 0.0-30.0 sec 3.33 GBytes 955 Mbits/sec
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
---
net/sched/sch_fifo.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
index e15a9eb..8dd27ec 100644
--- a/net/sched/sch_fifo.c
+++ b/net/sched/sch_fifo.c
@@ -54,7 +54,7 @@ static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
bool is_bfifo = sch->ops == &bfifo_qdisc_ops;
if (opt == NULL) {
- u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;
+ u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1000;
if (is_bfifo)
limit *= psched_mtu(qdisc_dev(sch));
--
1.7.12
.
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] pkt_sched: fix bandwidth's accuracy of software device with htb
2013-07-31 2:39 [PATCH] pkt_sched: fix bandwidth's accuracy of software device with htb Yang Yingliang
@ 2013-07-31 3:08 ` Eric Dumazet
0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2013-07-31 3:08 UTC (permalink / raw)
To: Yang Yingliang; +Cc: Jamal Hadi Salim, David S. Miller, netdev
On Wed, 2013-07-31 at 10:39 +0800, Yang Yingliang wrote:
> When we set bandwidth on the software devices with htb,
> it's not precise.
>
> With htb, sch->limit is set from devices TX queue's
> length that is not 0. Because software devices TX
> queue is 0, sch->limit is set to default value 1.
>
> Because the length of skb_buff queue is bigger than
> sch->limit whose value is 1, some packets are dropped.
> This leads to software devices can't make full use of
> the bandwidth and influence the accuracy.
>
> To fix this issue, set the default value of sch->limit
> to 1000 that is the value of eth device's tx_queueu_len.
>
> Example:
> tc qdisc add dev bond0 root handle 1: htb default 1
> tc class add dev bond0 parent 1:0 classid 1:1 htb rate 1Gbit ceil 1Gbit
> iperf -c host -t 30 -i 10
>
> With old sch->limit:
> [ ID] Interval Transfer Bandwidth
> [ 3] 0.0-10.0 sec 579 MBytes 486 Mbits/sec
> [ 3] 10.0-20.0 sec 604 MBytes 507 Mbits/sec
> [ 3] 20.0-30.0 sec 551 MBytes 462 Mbits/sec
> [ 3] 0.0-30.0 sec 1.69 GBytes 485 Mbits/sec
>
> With new sch->limit:
> [ ID] Interval Transfer Bandwidth
> [ 3] 0.0-10.0 sec 1.11 GBytes 955 Mbits/sec
> [ 3] 10.0-20.0 sec 1.11 GBytes 955 Mbits/sec
> [ 3] 20.0-30.0 sec 1.11 GBytes 955 Mbits/sec
> [ 3] 0.0-30.0 sec 3.33 GBytes 955 Mbits/sec
>
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---
> net/sched/sch_fifo.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sched/sch_fifo.c b/net/sched/sch_fifo.c
> index e15a9eb..8dd27ec 100644
> --- a/net/sched/sch_fifo.c
> +++ b/net/sched/sch_fifo.c
> @@ -54,7 +54,7 @@ static int fifo_init(struct Qdisc *sch, struct nlattr *opt)
> bool is_bfifo = sch->ops == &bfifo_qdisc_ops;
>
> if (opt == NULL) {
> - u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1;
> + u32 limit = qdisc_dev(sch)->tx_queue_len ? : 1000;
>
> if (is_bfifo)
> limit *= psched_mtu(qdisc_dev(sch));
Hmm. This looks like user error to me.
What if existing scripts relied on the limit being 1 ?
If you want to use pfifo on a virtual device, while not setting explicit
limit, you have to "ifconfig bond0 txqueuelen 1000"
Seriously, using pfifo or bfifo without setting explicit plimit/blimit
is not very safe, even with non virtual devices.
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2013-07-31 3:08 ` Eric Dumazet
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