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Very impressive. In your RPi4 experiments would you benefit from having more DRAM if you didn't have the 1GB limit? I'm wondering how much difference the gic makes. Do you think there is a way to breakdown the performance uplift?

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More RAM could help us with a scale test, or maybe with a storage-related benchmark.

Regarding the GIC, first I think we should spend some time examining the benefits from the A72 upgrade. Then, breaking down the time spent on each step of the VM lifecycle should be fairly straightforward (annotate EL changes, capture numbers with perf or something similar).

I have two 4 GB RPi4s, and can run any tests if you like.

Or is this about some 1GB barrier DMA limitation?

I did notice VideoCore can only access maximum 1GB of RAM. Related to that?

the issue about the available RAM is this: https://github.com/raspberrypi/linux/commit/cdb78ce891f6c636...

probably some kind of address mapping, but I'm no expert on this stuff ;-)

Saw that, but that doesn't really tell why, and how much effort is required to solve this. Maybe SD stuff is in the VideoCore side, and it simply can't DMA above 1 GB limit, and requires to have below 1GB DMA buffers + copy for transfers to upper memory. Maybe.

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