umaplehurst
commented
4 years ago Also see heavy CPU loading here when doing RX load testing. Unfortunately, SPI on Linux is rather high-overhead. Every time you call the SPI core with a request, it costs you, so anything that can be done to group together or reduce the number of requests helps.
Reviewing the driver, there is one easy optimization that can be made, which is to reduce the number of separate SPI core requests when setting the UINC bit in the RX FIFO, and to instead batch them up into a single SPI core request. I'm attaching a rough quick patch, might need to be made more pretty but Marc can first comment whether this sort of thing feels acceptable... mcp25xxfd-rx-fifo-finalize.txt
marckleinebudde
ghost
Hello, thank you for your effort on improving this CAN driver! I have a question on CPU load that I observe doing tests under load. With just over 3000 inbound frames per second the irq process consumes over 47% CPU and spi process consumes over 24% CPU running on CM 3+.
In my project we plan to disable dynamic frequency for CM to have more predictable behavior, and when we do that these two processes consume more than a full core just receiving this data stream.
Is there a way to optimize this or is there a fundamental reason why this cannot be optimized?