I've revisited my testing, and found I was wrong about the packets getting stuck in the FEC queue. The packets are getting stuck in the bestcomm.
I generate a timestamp for each skb's ip_hdr->id at the beginning of mpc52xx_fec_start_xmit, and for each skb retrieved from the bestcomm. Typically the packets make it through bestcomm in under 200us. But sometimes a single packet will sit in bestcomm until the next packet added. In the case of a delayed ACK this can be around 400ms. When I look at the state of the registers when this condition is detected (before adding the next bd): tx_dmatsk->flags = 1 tcr[1] = 0x20c1 Both of these values seem to indicate the the TX task is disabled. I'm pretty sure that nothing in the kernel is disabling the task, so it must be an automatic behavior. I notice that bcom_submit_next_buffer() checks the task->flags and if the LSB is set it enables the task. So I'm guessing that is what gets things moving again when the freeze happens. My best guess is this is a race condition between the driver and the dma controller. Is there any risk to just calling bcom_enable(tsk). Maybe after a short sleep. Joey Nelson _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
