* [PATCH 1/1] cbq: incorrect processing of high limits
@ 2013-04-01 13:01 Vasily Averin
2013-04-01 16:24 ` Eric Dumazet
0 siblings, 1 reply; 3+ messages in thread
From: Vasily Averin @ 2013-04-01 13:01 UTC (permalink / raw)
To: netdev; +Cc: Alexey Kuznetsov, David S. Miller, Jamal Hadi Salim
currently cbq works incorrectly for limits > 10% real link bandwidth,
and practically does not work for limits > 50% real link bandwidth.
Below are results of experiments taken on 1 Gbit link
In shaper | Actual Result
-----------+---------------
100M | 108 Mbps
200M | 244 Mbps
300M | 412 Mbps
500M | 893 Mbps
This happen because of q->now changes incorrectly in cbq_dequeue():
when it is called before real end of packet transmitting,
L2T is greater than real time delay, q_now gets an extra boost
but never compensate it.
To fix this problem we prevent change of q->now until its synchronization
with real time.
Signed-off-by: Vasily Averin <vvs@openvz.org>
Reviewed-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
---
net/sched/sch_cbq.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
index 6aabd77..5b5c83a 100644
--- a/net/sched/sch_cbq.c
+++ b/net/sched/sch_cbq.c
@@ -962,8 +962,11 @@ cbq_dequeue(struct Qdisc *sch)
cbq_update(q);
if ((incr -= incr2) < 0)
incr = 0;
+ q->now += incr;
+ } else {
+ if (now > q->now)
+ q->now = now;
}
- q->now += incr;
q->now_rt = now;
for (;;) {
--
1.7.5.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 1/1] cbq: incorrect processing of high limits
2013-04-01 13:01 [PATCH 1/1] cbq: incorrect processing of high limits Vasily Averin
@ 2013-04-01 16:24 ` Eric Dumazet
2013-04-02 18:30 ` David Miller
0 siblings, 1 reply; 3+ messages in thread
From: Eric Dumazet @ 2013-04-01 16:24 UTC (permalink / raw)
To: Vasily Averin; +Cc: netdev, Alexey Kuznetsov, David S. Miller, Jamal Hadi Salim
On Mon, 2013-04-01 at 17:01 +0400, Vasily Averin wrote:
> currently cbq works incorrectly for limits > 10% real link bandwidth,
> and practically does not work for limits > 50% real link bandwidth.
> Below are results of experiments taken on 1 Gbit link
>
> In shaper | Actual Result
> -----------+---------------
> 100M | 108 Mbps
> 200M | 244 Mbps
> 300M | 412 Mbps
> 500M | 893 Mbps
>
> This happen because of q->now changes incorrectly in cbq_dequeue():
> when it is called before real end of packet transmitting,
> L2T is greater than real time delay, q_now gets an extra boost
> but never compensate it.
>
> To fix this problem we prevent change of q->now until its synchronization
> with real time.
>
> Signed-off-by: Vasily Averin <vvs@openvz.org>
> Reviewed-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
> ---
> net/sched/sch_cbq.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/net/sched/sch_cbq.c b/net/sched/sch_cbq.c
> index 6aabd77..5b5c83a 100644
> --- a/net/sched/sch_cbq.c
> +++ b/net/sched/sch_cbq.c
> @@ -962,8 +962,11 @@ cbq_dequeue(struct Qdisc *sch)
> cbq_update(q);
> if ((incr -= incr2) < 0)
> incr = 0;
> + q->now += incr;
> + } else {
> + if (now > q->now)
> + q->now = now;
> }
> - q->now += incr;
> q->now_rt = now;
>
> for (;;) {
Acked-by: Eric Dumazet <edumazet@google.com>
Still, after your patch a limit of 500Mbit gives :
rate 515872Kbit 946pps backlog 0b 2p requeues 0
HTB is more precise :
rate 500667Kbit 41336pps backlog 0b 2p requeues 0
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 1/1] cbq: incorrect processing of high limits
2013-04-01 16:24 ` Eric Dumazet
@ 2013-04-02 18:30 ` David Miller
0 siblings, 0 replies; 3+ messages in thread
From: David Miller @ 2013-04-02 18:30 UTC (permalink / raw)
To: eric.dumazet; +Cc: vvs, netdev, kuznet, jhs
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 01 Apr 2013 09:24:36 -0700
> On Mon, 2013-04-01 at 17:01 +0400, Vasily Averin wrote:
>> currently cbq works incorrectly for limits > 10% real link bandwidth,
>> and practically does not work for limits > 50% real link bandwidth.
>> Below are results of experiments taken on 1 Gbit link
>>
>> In shaper | Actual Result
>> -----------+---------------
>> 100M | 108 Mbps
>> 200M | 244 Mbps
>> 300M | 412 Mbps
>> 500M | 893 Mbps
>>
>> This happen because of q->now changes incorrectly in cbq_dequeue():
>> when it is called before real end of packet transmitting,
>> L2T is greater than real time delay, q_now gets an extra boost
>> but never compensate it.
>>
>> To fix this problem we prevent change of q->now until its synchronization
>> with real time.
>>
>> Signed-off-by: Vasily Averin <vvs@openvz.org>
>> Reviewed-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
...
> Acked-by: Eric Dumazet <edumazet@google.com>
Applied, thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2013-04-01 13:01 [PATCH 1/1] cbq: incorrect processing of high limits Vasily Averin
2013-04-01 16:24 ` Eric Dumazet
2013-04-02 18:30 ` David Miller
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