The recent bootloader change removes the difference in time taken for refresh between 4G and 8G Pi5.
In theory 4G and 8G will now have the same performance.
But like most things, its a bit more complicated than that.
We typically use dual rank sdram chips, where the highest used address bit changes the rank.
Using both ranks has some benefits as you effectively can have more open pages.
This can mean having "too much" sdram may result in the top half of ram being unused and can
lose the benefit of the extra open pages in the second rank.
You need a fairly specific workload to show this difference.
Use too little sdram and both 4G and 8G look the same.
Too much (i.e. starting to swap) and 8G wins by a mile.
The NUMA patches avoid these issues,
and make both 4G and 8G Pi5 significantly faster (and I'd expect no clear difference between them).
In theory 4G and 8G will now have the same performance.
But like most things, its a bit more complicated than that.
We typically use dual rank sdram chips, where the highest used address bit changes the rank.
Using both ranks has some benefits as you effectively can have more open pages.
This can mean having "too much" sdram may result in the top half of ram being unused and can
lose the benefit of the extra open pages in the second rank.
You need a fairly specific workload to show this difference.
Use too little sdram and both 4G and 8G look the same.
Too much (i.e. starting to swap) and 8G wins by a mile.
The NUMA patches avoid these issues,
and make both 4G and 8G Pi5 significantly faster (and I'd expect no clear difference between them).
Statistics: Posted by dom — Sat Aug 17, 2024 1:05 pm