Jose Blanquicet <[email protected]> writes: > 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.
What speeds were you getting without shaping? > 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. Hmm, are you actually running out of CPU? I.e., is the CPU pegged at 100% when you hit this limit? What kind of platform are you running on? And what kernel and CAKE versions are you using? > 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? No, you've already turned off most of the features that might incur overhead, so I don't think there's anything more you can do configuration-wise to improve CPU load. Shaping does tend to use up a lot of CPU, so it's not too surprising you run into issues here. We did recently get a pull request whose author states that he was seeing a 1/3 improvement in performance from it. See: https://github.com/dtaht/sch_cake/pull/136 You could try this; if your ingress network device driver has the same issue with skbs being allocated in smaller bits, you may see a similar increase with this patch. For a quick test you could also just try commenting out the call to cake_handle_diffserv() entirely since you're running in besteffort mode anyway :) -Toke _______________________________________________ Cake mailing list [email protected] https://lists.bufferbloat.net/listinfo/cake
