Re: IPC drop down on AMD epyc 7702P

[Jean-Baptiste Roquefere <jb.roquefere@ateme.com>]

Hello Prateek,
long time no see... I've been very busy lately.

Did he try with relax_domain_level=3, i.e. prevent newilde idle


>> balance between LLC ? I don't see results showing that it's not enough
>> to prevent newly idle migration between LLC
>
> I don't think he did. JB if it isn't too much trouble, could you please
> try running with "relax_domain_level=3" in kernel cmdline and see if
> the performance is similar to "relax_domain_level=2".

I just tried relax_domain_level=3 on my payload. As you can see 
relax_domain_level=3 performances are more or less the same

+--------------------+---------------------+---------------------+
| Kernel             | 6.12.17 relax dom 2 | 6.12.17 relax dom 3 |
+--------------------+---------------------+---------------------+
| Utilization (%)    | 52,01               | 52,15 |
| CPU effective freq | 1 294,12            | 1 309,85 |
| IPC                | 1,42                | 1,40 |
| L2 access (pti)    | 38,18               | 38,03 |
| L2 miss   (pti)    | 7,78                | 7,90 |
| L3 miss   (abs)    | 33 929 609 924,00   | 33 705 899 797,00 |
| Mem (GB/s)         | 49,10               | 48,91 |
| Context switches   | 107 896 729,00      | 106 441 463,00 |
| CPU migrations     | 16 075 947,00       | 18 129 700,00 |
| Real time (s)      | 193,39              | 193,41 |
+--------------------+---------------------+---------------------+

We got the point that tuning this variable is not a good solution, but 
for now it's the only one we can apply.

Without this tuning our solution loses real time video processing. With 
: we keep real time on.


Thanks for your help, I'll stay alert on this thread if someday a better 
solution can emerge.


Regards,


jb