Well you only have soo many shared ressources and if it is not
additional exits/interrupts then it is contention on shared ressources.

We are probably talking about caches, TLBs and buses.

You should be able to use i.e. "perf" on Linux to read out hardware
performance counters. And there you might want to look for TLB and
cache misses.

But the bisecting might be the better idea. Jan already mentioned the
"features" that could be responsible. With a bit of educated guessing
you will get away with just a few tries.

Henning

Am Fri, 25 Oct 2019 00:04:36 -0700
schrieb Chung-Fan Yang <sonic.tw...@gmail.com>:

> Alright, I have test the latency from HW IRQ to application response.
> 
> I found out that there aren't any additional VM-Exit or IRQ, nor RTOS 
> scheduling and house-keeping.
> 
> It feels like the processor is generally slower as everything takes
> longer to run.
> 
> The IRQ epilogue takes ~7.8us and iretq ~2.x us. In addition, the
> libc and syscall interface also have slow downed a bit.
> 
> I do notice after upgrading, even with CAT, my RTOS latency are prone
> to be influenced by the Linux side applications.
> This was not observed during v0.9.1.
> 
> It's strange.
> 
> 
> Yang.
> 



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