I tested SGI interrupt latency, it seems that GIC3.0's SGI interrupt latency are much bigger than GIC2.0.
How to test:
1. read timestamp(t01)
2. core0 write ICC_SGI0R_EL1 to trigger core1, read timestamp(t02)
3. isr in core1, read timestamp(t03)
1. read timestamp(t11)
2. core0 write GICD_SGIR to trigger core1, read timestamp(t12)
3. isr in core1, read timestamp(t13)
Result is (had think about the time of reading timestamp):
1. (t02 - t01) nearly 3 times bigger than (t12 - t11) which means system register cost more time than access to memory mapped memory.
2. (t03 - t02) nearly 2 times bigger than (t13 - t12) which means interrupt latency of GIC3.0 are much bigger than GIC 2.0
Is this normal? Any help will be appreciated! Thanks!
Which cores? The same on both SoCs? The same bus clock? You should provide some basic information. And/or ask yourself what influences your meassurements.
Sorry for my negligence!
Both are ARM Cortex-A53 SMP 4 cores.
The clock with GIC3.0 are lower about 10% than the one with GIC2.0.
But this can not lead to 2-3 times decline. Do you agree?
What are the times you are measuring?
I changed timer to ARM counter CNTVCT_EL0, which is more common.
This is new tests result:
from write trigger to int enter(assembly entry) = 0.96us
from int enter to int service = 0.48usGIC2.0:
from write trigger to int enter(assembly entry) = 0.15us
from int enter to int service = 0.58us
So, we can see from int enter to int service are nearly same.But from write trigger to int enter(assembly entry) of GIC3.0 are much bigger than GIC2.0.
Did ARM test these parameters? I think maybe it is related to the hardware architecture?
I tried it on a Zynq US+, but this is a GIC V2 as I see now. I got 0.29us from trigger to IS-process.
I have an i.MX8 on desk, but NXP is not clear which GIC they use: They write about v4 and v3?!
You can check GICD_PIDR2 register.
GICD_PIDR2 bits [7:4] ArchRev will tell whether it is v3 or v4 or v2.
By the way, what timer did you use for counting?
I used the generic timer (CNTPCNT_EL0) running at 100MHz.
Did you have any new test results?
Sorry, no. I have to make a BSP first for the i.MX8.