xmit_wait - lost BW gauge

[phatut]

Using the port_xmit_wait counter available in the sysfs IB counters we can assess the lost BW on the port. This will probably be used with the tool's sample time, enabling us to see the congestion on a per-sample basis.

The conversion formula depends on the generation - but we'll concentrate on the newer gens which uses the same formula:

Lost Bytes can be determined by the device's generation (Modern generations set the tick to 7, legacy will use 31).

Bottom line - for newer gens, you should be using the formula:

(port_xmit_wait[t2-t1] * (7+1) * 8) / (sample_time [t2-t1] * 1E-9)

LMK if you have any questions.

[vinjn]

@meow-watermelon

[meow-watermelon]

thanks @vinjn for the reminder!

@phatut - as we discussed offline, could you pls. list detailed supported device IDs here? though there are some mainstream devices that we know, it's still better we can have a detailed source-of-truth device IDs.

thanks.