Deal with negative feed back loop in DA gas price

[MitchTurner]

Linked Issues/PRs

#2347

Description

/// Because the DA gas price can increase even when no-one is using the network, there is a potential
/// for a negative feedback loop to occur where the gas price increases, further decreasing activity
/// and increasing the gas price. The `L2ActivityTracker` is used to moderate changes to the DA
/// gas price based on the activity of the L2 chain.
///
/// For each L2 block, the activity is calculated as a percentage of the block capacity used. If the
/// activity is below a certain threshold, the activity is decreased. The activity exists on a scale
/// between 0 and the sum of the increase, hold, and decrease buffers.
///
/// e.g. if the decrease range is 50, the hold range is 50, and the increase range is 50:
///
/// 0<-- decrease range -->50<-- hold range -->100<-- increase range -->150
///
/// The current activity determines the behavior of the DA gas price.
///
/// For healthy behavior, the activity should be in the `increase` range.

Checklist

• New behavior is reflected in tests

Before requesting review

• I have reviewed the code myself

[netrome]

Nice stuff! A few suggestions from my end.

[AurelienFT]

Do you have an idea of the value you want to put in the threshold. You are saying that we should aim to be in normal range but right now on Ignition there is only 0 or 1 tx per block (excluding mint tx) and so the threshold seems hard to find given this granularity (0 or 1) and I'm having hard times to understand how we can maintain normal range in these conditions

[MitchTurner]

Do you have an idea of the value you want to put in the threshold.

In a healthy network, I would want to keep it low, like 5% or 10%. We won't know for sure until we have a lot more data though.

You are saying that we should aim to be in normal range but right now on Ignition there is only 0 or 1 tx per block (excluding mint tx) and so the threshold seems hard to find given this granularity (0 or 1) and I'm having hard times to understand how we can maintain normal range in these conditions

This is a very good point. But safety mode only comes into play if we are trying to increase the gas price (we are unprofitable). Currently, the cost of posting blobs is so low that even if the DA gas price is set to the minimum, it will might still be profitable for us. Also, until the network gets more active, I think we should just swallow the costs of DA as a business. So, it's fine if most blocks are below the threshold.

[netrome]

The L2ActivityTracker needs a small update to reflect the new parameters. Otherwise this looks good to me.

[rafal-ch]

LGTM 👍

[rafal-ch]

Re-approving 👍

[AurelienFT]

Even more test youhouuu