[vladvasiliu]

This is interesting. I'm getting much worse results on an i7-1165G7 than the ones published:

    Num cores: 8
    Using RDTSC to measure time: true
    Num round trips per samples: 5000
    Num samples: 300
    Showing latency=round-trip-time/2 in nanoseconds:

       0       1       2       3       4       5       6       7
  0
  1   70±1
  2   53±1    42±0
  3   73±5   134±5    80±1
  4   16±0    49±1    56±1    46±1
  5   63±4    28±1   128±5    67±1    66±1
  6   56±1    49±1    10±0    81±4   124±4    72±1
  7   57±1    57±1    45±1    10±0    63±4   130±5    87±1

    Min  latency: 10.1ns ±0.2 cores: (6,2)
    Max  latency: 134.1ns ±5.3 cores: (3,1)
    Mean latency: 64.7ns

[consp]

Might too-aggressive power saving be an issue? The spikes (100+ns) are all hyper-threads. edit: No, 4 to 6 is not a HT.

[vladvasiliu]

I was thinking some kind of throttling, yes. I've always found this particular laptop (HP EliteBook 840 G8) surprisingly slow.

If that's the case, I think it kicks in quickly because running this with 500, 5_000 and 50_000 round trips gives results in the same ballpark.

There doesn't seem to be any difference between performance and powersave governors for this particular test.