netdev - Re: HTB going crazy over ~5Gbit/s (4.12.9, but problem present in older kernels as well)

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Date:   Wed, 13 Sep 2017 09:55:47 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Denys Fedoryshchenko <nuclearcat@...learcat.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: HTB going crazy over ~5Gbit/s (4.12.9, but problem present in
 older kernels as well)

On Wed, 2017-09-13 at 09:42 -0700, Eric Dumazet wrote:
> On Wed, 2017-09-13 at 19:27 +0300, Denys Fedoryshchenko wrote:
> > On 2017-09-13 19:16, Eric Dumazet wrote:
> > > On Wed, 2017-09-13 at 18:34 +0300, Denys Fedoryshchenko wrote:
> > >> Well, probably i am answering my own question, removing estimator from
> > >> classes seems drastically improve situation.
> > >> It seems estimator has some issues that cause shaper to behave
> > >> incorrectly (throttling traffic while it should not).
> > >> But i guess thats a bug?
> > >> As i was not able to predict such bottleneck by CPU load measurements.
> > > 
> > > Well, there was a reason we disabled HTB class estimators by default ;)
> > > 
> > > 
> > > https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=64153ce0a7b61b2a5cacb01805cbf670142339e9
> > 
> > As soon as disabling it solve my problem - i'm fine, hehe, but i guess 
> > other people who might hit this problem, should be aware how to find 
> > reason.
> > They should not be disappointed in Linux :)
> 
> Well, if they enable rate estimators while kernel does not set them by
> default, they get what they want, at a cost.
> 
> > Because i can't measure this bottleneck before it happens, i'm seeing on 
> > mpstat all cpu's are idle, and same time traffic is throttled.
> 
> Normally things were supposed to get much better in linux-4.10
> 
> ( https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=1c0d32fde5bdf1184bc274f864c09799278a1114 )
> 
> But I apparently added a scaling bug.
> 
> I will try :
> 
> diff --git a/net/core/gen_estimator.c b/net/core/gen_estimator.c
> index 0385dece1f6fe5e26df1ce5f40956a79a2eebbf4..7c1ffd6f950172c1915d8e5fa2b5e3f77e4f4c78 100644
> --- a/net/core/gen_estimator.c
> +++ b/net/core/gen_estimator.c
> @@ -83,10 +83,10 @@ static void est_timer(unsigned long arg)
>         u64 rate, brate;
>  
>         est_fetch_counters(est, &b);
> -       brate = (b.bytes - est->last_bytes) << (8 - est->ewma_log);
> +       brate = (b.bytes - est->last_bytes) << (10 - est->ewma_log - est->intvl_log);
>         brate -= (est->avbps >> est->ewma_log);
>  
> -       rate = (u64)(b.packets - est->last_packets) << (8 - est->ewma_log);
> +       rate = (u64)(b.packets - est->last_packets) << (10 - est->ewma_log - est->intvl_log);
>         rate -= (est->avpps >> est->ewma_log);
>  
>         write_seqcount_begin(&est->seq);


Much better indeed

# tc -s -d class sh dev eth0 classid 7002:11 ; sleep 10 ;tc -s -d class
sh dev eth0 classid 7002:11

class htb 7002:11 parent 7002:1 prio 5 quantum 200000 rate 5Gbit ceil
5Gbit linklayer ethernet burst 80000b/1 mpu 0b cburst 80000b/1 mpu 0b
level 0 rate_handle 1 
 Sent 389085117074 bytes 256991500 pkt (dropped 0, overlimits 5926926
requeues 0) 
 rate 4999Mbit 412762pps backlog 136260b 2p requeues 0 
 TCP pkts/rtx 256991584/0 bytes 389085252840/0
 lended: 5961250 borrowed: 0 giants: 0
 tokens: -1664 ctokens: -1664

class htb 7002:11 parent 7002:1 prio 5 quantum 200000 rate 5Gbit ceil
5Gbit linklayer ethernet burst 80000b/1 mpu 0b cburst 80000b/1 mpu 0b
level 0 rate_handle 1 
 Sent 395336315580 bytes 261120429 pkt (dropped 0, overlimits 6021776
requeues 0) 
 rate 4999Mbit 412788pps backlog 68Kb 2p requeues 0 
 TCP pkts/rtx 261120469/0 bytes 395336384730/0
 lended: 6056793 borrowed: 0 giants: 0
 tokens: -1478 ctokens: -1478


echo "(395336315580-389085117074)/10*8" | bc
5000958800