I ask this because I noticed even the no-op instruction uses a some compute units (I assume for loading the program and stuff like this) and it made me wonder. Is there a lower bound? Is it zero?
2 Answers
Depends on how deep you want to go. I won't be able to give an exact number, but hopefully a picture can be painted here. Theoretically the very minimum would be 1 CU (to my knowledge every transaction has to actually do something), but in reality most transactions will use at least 1 syscall. For example "sol_log" uses about 100 CUs in an assembly program. A standard entrypoint in a program (using C or Rust) will normally log a fair bit of compute usage as well.
A good representation of this would be the sbpf-inline-asm example from Dean Little. He uses some basic asm instructions + the sol_log syscall. This logs at 104 CUs iirc (most from the logging), and to date it's probably the smallest program I've ever seen by that metric.
EDIT: I linked the wrong repo. The correct one I was referring to is this
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This is helpful, thank you! I'm asking mostly from a theoretical standpoint (partially to help me answer solana.stackexchange.com/questions/14701/…), so the program can be completely useless as long as the transaction would pass onchain. Judging from the asm example, the minimum would be 1 CU by just doing a
movfor example correct?– McBainCommented Jun 12 at 20:22 -
@Ahri custom entrypoint (similar to link above) -> single operation -> exit would use about 1 CU. This is also assuming no instruction data provided (not sure if loading that into memory would add more CUs) Commented Jun 13 at 13:33
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If your program just calls exit, then it's possible for the program to only take 1 CU. Currently, there's no CU cost to instruction data, loading account data, or taking write locks, but that might change in the future.
Here's that example:
#[no_mangle]
pub extern "C" fn entrypoint(_: *mut u8) -> () {
}
#[no_mangle]
fn custom_panic(_info: &core::panic::PanicInfo<'_>) {}
solana_program::custom_heap_default!();
If you dump the program, then you'll see the singular call to exit:
$ ~/.local/share/solana/install/active_release/bin/sdk/sbf/scripts/dump.sh target/deploy/program.so out.txt
$ cat out.txt
... loads of other stuff ...
Disassembly of section .text
0000000000000120 <entrypoint>
36 95 00 00 00 00 00 00 00 exit
