Re: [RFC v2 net-next 00/10] Time based packet transmission

Hi,


On 01/22/2018 09:26 PM, Richard Cochran wrote:

On Mon, Jan 22, 2018 at 09:23:27PM -0800, Richard Cochran wrote:

quoted

On Wed, Jan 17, 2018 at 03:06:11PM -0800, Jesus Sanchez-Palencia wrote:

quoted

First, a baseline test was ran for 10 minutes with the plain kernel only:

|                 | plain kernel @ 1ms |
|-----------------+--------------------+
| min (ns):       |    +4.820000e+02   |
| max (ns):       |    +9.999300e+05   |
| pk-pk:          |    +9.994480e+05   |

...

quoted

|                 |    tbs SW @ 1ms   |  tbs HW @ 1ms  | tbs HW @ 250 us |
|-----------------+-------------------+----------------+-----------------|
| min (ns):       |    +1.510000e+02  |  +4.420000e+02 |   +4.260000e+02 |
| max (ns):       |    +9.977030e+05  |  +5.060000e+02 |   +5.060000e+02 |
| pk-pk:          |    +9.975520e+05  |  +6.400000e+01 |   +8.000000e+01 |

I wonder about these worst case measurements of 999 and 998
milliseconds.  It almost looks like you missed one entire period.

  ^^^^
microseconds

quoted

Could this simply be a bug in the test setup?

Yes. From the data set of the tbs SW:

offset |      timestamp
-------+---------------------
(...)  |
10639  | 1516117448.058010639
9503   | 1516117448.059009503
10167  | 1516117448.060010167
9823   | 1516117448.061009823
9567   | 1516117448.062009567
997703 | 1516117448.062997703 ****
911719 | 1516117448.063911719
12655  | 1516117448.065012655
12399  | 1516117448.066012399
(...)

Since the period was 1ms, the highlighted entry should have arrived within the
[1516117448.063000000, 1516117448.063999999] range, so in this case it was
early. For the next runs, I will modify the test setup so the txtime is sent as
part of the packet payload and later taken into account by the post-processing
script that is calculating the offsets.


Thanks,
Jesus

quoted

Thanks,
Richard