cmd/geth: add flag --dev.gaslimit for dev mode

[jessetane]

I was trying to tinker with some large gas limits to speed up some contract tests and while --miner.gaslimit does work, it takes a long time to reach if the initial gas limit is much lower.

[jwasinger]

Might it be sufficient to use --dev.period=1 (which will cause the miner to seal 1 block / second)? This would allow to bump up the gas limit more quickly.

[jessetane]

Just tried - the gas limit does not seem to come up faster? Maybe I'm missing something else. Also the 1s pause between each block slows everything else down so even if it did I'm not sure it would be a net gain.

I assume the recommended approach here is to roll my own genesis file? I guess that's not too bad but dev mode is otherwise pretty convenient..

Maybe an alternate take on this could be to initialize dev mode at --miner.gaslimit if it's set?

[holiman]

LGTM

[karalabe]

Should we just bump the default gas limit to 30M in dev mode?

[holiman]

Should we just bump the default gas limit to 30M in dev mode?

We could do that, but I can see some value in being able to test arbitrarily gigantic blocks in devmode. I don't have a strong opinion though

[jessetane]

Just for some additional detail, I wanted to generate a large / complex fixture in eth state to run my test against and used this flag with a limit of 1B to complete the setup quickly.