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drivers/usbdev/cdcncm: send TX immediately instead of after a tick-quantized delay #19469

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drivers/usbdev/cdcncm: send TX immediately instead of after a tick-quantized delay #19469

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14 changes: 12 additions & 2 deletions drivers/usbdev/cdcncm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1302,8 +1302,18 @@ static int cdcncm_send(FAR struct netdev_lowerhalf_s *dev, FAR netpkt_t *pkt)
}
else
{
work_queue(ETHWORK, &self->delaywork, cdcncm_transmit_work, self,
MSEC2TICK(CDCNCM_DGRAM_COMBINE_PERIOD));
/* Defer the transmit to the work thread so the caller is not blocked
* on wrreq_idle, but do so with ZERO delay. A non-zero delay here is
* quantized to the system tick: MSEC2TICK(1) rounds *up* to a full
* tick (10ms at the default 100Hz), so the reply to every single
* datagram (ping, TCP ACK, one-MSS HTTP segment) was being held for
* 10-20ms, dominating the USB-NIC round-trip time. Delay 0 wakes the
* work thread immediately (sub-ms) while still coalescing any further
* datagrams that the network stack appends in the same TX burst before
* the worker gets to run.
*/

work_queue(ETHWORK, &self->delaywork, cdcncm_transmit_work, self, 0);
}

return OK;
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