A bit of the background: We are using Jetson Nano production modules for our project. We use custom carrier boards for flashing the Nanos, which do not have an HDMI support, nor any other way to verify serial logs at startup/any time. The kernel for Jetson Nano did not initially have support for SD card. From this forum, I managed to get information to generate the patch for the SD card support. But after applying this patch, it was observed that the boot time was slow. To fix this, again from the information obtained on this forum, I created a patch in which I disable CRC checks for SD card and also HDMI support (as we are not using it). Besides this, I also pass the partition on which root is to be found (/dev/mmcblk0p1) as command line argument to the kernel via a conf.common file before flashing. Please find attached the two patches.
The problem we are now facing is that the reads and writes from and to the SD card are extremely slow on the Nano. Gnome-disks benchmark test reported a (surprisingly constant) speed of 1.5 MBps for read and write. The SD cards we use are SanDisk Extreme microSD UHS-I V30, for which on an Ubuntu desktop, the read and write speeds are always above 45 MBps. Please find below the output of the command:
cat /sys/kernel/debug/mmc1 when run on the Nano:
clock: 50000000 Hz vdd: 21 (3.3 ~ 3.4 V) bus mode: 2 (push-pull) chip select: 0 (don't care) power mode: 2 (on) bus width: 2 (4 bits) timing spec: 2 (sd high-speed) signal voltage: 0 (3.30 V) driver type: 0 (driver type B)
Any pointers regarding this? It seems there is a (undesired) cap on the read/write speeds to the SD card. The SD card device is located at /dev/mmcblk1. We use an ext4 partitioning scheme.
Can the swap memory have something to do with this?
patches.zip (2.09 KB)