Re: Softirq priority inversion from "softirq: reduce latencies"

Sebastian Andrzej Siewior
2016-03-07T15:48:17Z

On 02/27/2016 07:19 PM, Peter Hurley wrote:
> Hi Eric,

Hi Peter,

> Because both the uart driver (omap8250) and the dmaengine driver
> (edma) were (relatively) new, we assumed there was some race between
> starting a new rx DMA and processing the previous one.

Now after digesting the whole thread. I complained about this a long
while ago. After you start RX-DMA the DMA-engine is not programmed
immediately but deferred into softirq/tasklet. This is not the case for
continuous DMA transfer - those are programmed right away.

I don't remember that I found a reason why this simple programming has
to be deferred and can't happen immediately like it is the case for the
continuous DMA transfers. So I skipped that. RX-DMA in UART was working
well but for some reason omap's MMC-card driver refused to work.

Sebastian