[i.MX6UL] CPU Usage 30-40% in Idle state

[john2207]

We are having i.MX6UL soc based custom board and AW-CM276NF WIFI card connected to usdhc1 (mmc@2190000). We have developed our BSP based on imx-5.10.9-1.0.0.xml NXP release. When we checked the CPU usage using (# htop -d1) command in our custom board, we noticed that idle case CPU usage is 30-40 %. When we run WIFI iperf test, then CPU usage is 95-100%.

The maximum throughput is 70~90Mbps(UpLoad), 40-50Mbps(DownLoad). The throughput data will not increase after the CPU is fully loaded 100%.

We have checked our BSP into i.MX6UL EVK board and observed that in idle case CPU usage is 30-40%. Also, we have flashed the i.MX6UL EVK demo images L5.10.9_1.0.0_MX6UL7D (https://www.nxp.com/webapp/sps/download/license.jsp?colCode=L5.10.9_1.0.0_MX6UL7D&appType=file1&DOWN...) and observed the same for idle case.

Can you please tell us whether 30-40% of CPU usage expected for idle case in i.MX6UL ? Because , we suspects that WIFI throughput not increased after loading CPU 100% related to that.

Also, the throughput is not to high as we expected. So , we suspects CPU is limiting the WIFI throughput.

We want to know that is it a HW limitation for IMX6UL ? Please provide your thoughts.

Attached screenshot , we took from i.MX6UL EVK with demo images. htop command not present in this BSP, we copied into target and ran it.

[igorpadykov]

Hi Janarthanam

in general one can look at defnition of System Idle mode in sect.6.2. System Idle mode (cpu clocks)

AN5170 i.MX 6UltraLite Power Consumption Measurement

Also may be useful to try mmdc profiling tool

https://source.codeaurora.org/external/imx/imx-test/tree/test/mmdc?h=lf-5.10.y_2.0.0

Best regards
igor

[john2207]

Hi @igorpadykov ,

We have one more update.

To debug further, we have run the iperf test and serial test application (https://github.com/cbrake/linux-serial-test) can transmit and receive data for 10 seconds in parallel and found that WIFI throughput dropped more immediately then back after 10 seconds serial test application completes. When both applications runs in parallel, CPU utilized 100%.

 We have marked the section in below screenshot where throughput drop more (ie., serial test runs at that time). When runs iperf alone, throughput is 40-50 Mbps. When runs along with serial application, it dropped even further below 20 Mbps. It indicates that , CPU is limiting the throughput.

[igorpadykov]

>The maximum throughput is 70~90Mbps(UpLoad), 40-50Mbps(DownLoad).

>The throughput data will not increase after the CPU is fully loaded 100%.

according to internal tests, maximum wifi throughput was about 35 Mbits,

so your figures are not bad.

Best regards
igor

[john2207]

Hi @igorpadykov ,

>>according to internal tests, maximum wifi throughput was about 35 Mbits,

Do you have throughput test report or data for i.MX6UL + WIFI chip ? If so, can you please share with us.

It would be helpful for us to compare.

[igorpadykov]

>Do you have throughput test report or data for i.MX6UL + WIFI chip ? If so, can you please share with us.

report: according to internal tests, maximum wifi throughput was about 35 Mbits,

Best regards
igor

[john2207]

Hi @igorpadykov ,

Please share us the below information ,

1. Which WIFI chip tested with i.MX6UL  SOC ? We are using AW-CM276NF wifi module.

2. What is the uSDHC clock frequency ? Is it 198 MHz ? For us , in 198 MHz  , ping and iperf test failed and wifi disconnects while doing ping or iperf test. But works well in 100 MHz

3. At which frequency throughput measured ? if you have any test log of throughput test, please share us.

We would need above information for comparison.

[igorpadykov]

tests were performed in Linux 3.14.38 per Release Notes included in  Documentation

AR6003 Wi-Fi supported in that release.

Best regards
igor