Hi Andrew,

On Thu, 2019-05-30 at 14:58 +0200, Andrew Lunn wrote:

On Thu, May 30, 2019 at 04:54:43PM +0800, Biao Huang wrote:

quoted

the default value of tx-frames is 25, it's too late when
passing tstamp to stack, then the ptp4l will fail:

ptp4l -i eth0 -f gPTP.cfg -m
ptp4l: selected /dev/ptp0 as PTP clock
ptp4l: port 1: INITIALIZING to LISTENING on INITIALIZE
ptp4l: port 0: INITIALIZING to LISTENING on INITIALIZE
ptp4l: port 1: link up
ptp4l: timed out while polling for tx timestamp
ptp4l: increasing tx_timestamp_timeout may correct this issue,
       but it is likely caused by a driver bug
ptp4l: port 1: send peer delay response failed
ptp4l: port 1: LISTENING to FAULTY on FAULT_DETECTED (FT_UNSPECIFIED)

ptp4l tests pass when changing the tx-frames from 25 to 1 with
ethtool -C option.
It should be fine to set tx-frames default value to 1, so ptp4l will pass
by default.

Hi Biao

What does this do to the number of interrupts? Do we get 25 times more
interrupts? Have you done any performance tests to see if this causes
performance regressions?

Yes, it seems tx-frames=25 can reduce interrupts.
But the tx interrupt is handled in napi now, which will disable/enable
tx interrupts at the beginning/ending of napi flow.

Here is the test result on our platform:
		tx-frames=1		tx-frames=25		
irq number	478514			393750	
performance	904Mbits/sec		902Mbits/sec

commands for test:
	"cat /proc/interrupts | grep eth0"
	"iperf3 -c ipaddress -w 256K -t 60"

Thanks to napi, the interrupts will not grow 25 times more(almost the
same level), and no obvious performance degradation.

Is there anybody can double check the performance with tx-frames = 0 or
25?

	    Andrew

Thanks.
Biao