taper of inflation is based on epoch 0, not the inflation activation epoch

[ryoqun]

Problem

taper of inflation is calculated as if the inflation was enabled since the very start of our cluster (genesis, epoch 0/slot 0). But it isn't true.

So, although initial interest rate is expected to be 15% at the start of inflation, it actually will be about ~14.28% without proper offsetting implementation:

solana/sdk/src/inflation.rs

Lines 25 to 27 in 0a7cbdf

	const DEFAULT_INITIAL: f64 = 0.15;
	const DEFAULT_TERMINAL: f64 = 0.015;
	const DEFAULT_TAPER: f64 = 0.15;

As far as I understand the token economy correctly, I think the planned initial inflation rate should be aligned with the time when the inflation is enabled, not the time of birth of our cluster.

Proposed Solution

Make it possible to take consider of inflation activation epoch?

CC: @ericlwilliams @mvines @rwalker-com

[ryoqun]

slightly related to this (w.r.t. inflation parameters): #5786 #10093

[rwalker-com]

assuming the network enables inflation soon, I think the fudge would probably be fine

another approach could be to increase inflation.initial so that it's actually 0.15 at inflation X

[ericlwilliams]

Yeah, I think Rob's suggestion would be fine (adjusting inflation.initial so that the inflation rate is what we want it to be when it turns on.
Keep in mind, 15% is just a placeholder and not likely the actual target (which will probably be around 6-9%). Depends on what the staking distribution looks like closer to inflation launch

[ryoqun]

@rwalker-com @ericlwilliams I see. Thanks for checking this! Then this issue will be just simple constant changing PR. :)

[mvines]

I think there's no explicit action needed here. As we finalize on the inflation rate we'll just adjust the initial values to match the desired % when inflation is activated