Usage of rte_latencystats

[Kamil Vojanec <vojanec@cesnet.cz>]

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Hello,

I was experimenting with measuring the latency of DPDK applications 
using the rte_latencystats module. While I could eventually get it to 
work somehow, I noticed some issues, that led me to the following questions:

1. How to measure latency on multicore systems? I noticed that there are 
a lot of global variables that store intermediate results of latency 
calculations. Also, the documentation suggests calling 
rte_latencystats_update() only on a single selected lcore.

2.  What is a good value to select for the `samp_intvl` parameter of 
rte_latencystats_init()? It seems that this option has a significant 
impact on the measured application's performance.

3. How often is it recommended to call rte_latencystats_update()? The 
documentation says the function needs to be called periodically, but 
never specifies how often. Should this be done in each processing loop?

4. Is there no way to clear the statistics? I noticed that the minimum 
and maximum measurement typically reaches some kind of static value that 
does not change and does not really reflect the dynamic nature of the 
measured system.

Looking forward to your reply,
Kamil Vojanec
CESNET, z.s.p.o.


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