[Cake] [CAKE] Rate is much lower than expected - CPU load is higher than expected

Y intruder_tkyf at yahoo.fr
Mon Jun 22 10:25:05 EDT 2020

You should paste this result.

tc -s qdisc show dev eth0


On 22/06/2020 22:10, Jose Blanquicet wrote:
> Hi everyone,
> We have an embedded system with limited CPU resources that acts as a
> gateway to provide Internet access from LTE to a private USB-NCM
> network (And also to a Wi-Fi private network but we will work on it
> later). Our problem is that the bandwidth on LTE and USB link is
> higher than what the system is able to handle thus it reaches 100% of
> CPU load when we perform a simple speed test from a device on the
> private network.
> Therefore, we want to limit the bandwidth to avoid system getting
> saturated in such use-case. To do so, we thought to use the CAKE on
> the USB interface. For instance, we tried:
>      tc qdisc replace root dev eth0 cake bandwidth 20mbit ethernet
> internet flowblind nonat besteffort nowash
> It worked correctly and the maximum rate was limited but there are two
> things that are worrying us:
> 1) The maximum rate reached after applying CAKE was in between 12Mbps
> and 15Mbps which is quite lower than the 20Mbps we are configuring, we
> were expecting around 18-19. Why? Is there something in the parameters
> we are doing wrong? Please take into account that our goal is to limit
> the rate but adding as little CPU load as possible.
> 2) The CPU load added by CAKE was not negligible for our system. In
> fact, we compared the CPU load when limitation was done by CAKE and by
> the device on the private network, e.g. curl tool with parameter
> "--limit-rate". As a result, we found that the CPU load when using
> CAKE was 30%. Is there any way to make it lighter with a different
> configuration?
> Thanks in advance for the support. Any suggestion is welcome.
> Jose Blanquicet
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