submit_windowed_post no need alway to check the proven_sectors length

[marco-storswift]

Proposal

windowpost message gasused are particularly high,

Background

I add gasused log in buildin-actors code. found the proven_sectors check can be optimized。

By example:

fvm_sdk::debug::log("xxxx  p1-13".to_string());
let proven_sectors = &post_result.sectors - &post_result.ignored_sectors;
if proven_sectors.is_empty() {
    // Abort verification if all sectors are (now) faults. There's nothing to prove.
    // It's not rational for a miner to submit a Window PoSt marking *all* non-faulty sectors as skipped,
    // since that will just cause them to pay a penalty at deadline end that would otherwise be zero
    // if they had *not* declared them.
    return Err(actor_error!(
        illegal_argument,
        "cannot prove partitions with no active sectors"
    ));
}
fvm_sdk::debug::log("xxxx  p1-14".to_string());

got the log like this

2022-09-08T11:32:05.097 ERROR fvm::kernel::default > AL: xxxx  p1-13; gas: 19823935.500
2022-09-08T11:32:05.097 ERROR fvm::kernel::default > AL: xxxx  p1-14; gas: 19841139.500

but post_result.ignored_sectors is empy normal, we shoud check the ignored_sectors length first. it can save gas

[coder-lb]

Usually post_result.ignored_sectors is empty. The subtraction of Bitfield needs many CPU cycles. So checking it before subtraction is an optimization method.

[Stebalien]

Yeah, that works. But it would be nicer to just optimize that subtraction. But that's tricker.

[Stebalien]

Try running benchmarks with https://github.com/filecoin-project/ref-fvm/pull/849.

[marco-storswift]

@Stebalien I used the https://github.com/filecoin-project/ref-fvm/pull/849. the result is very nice, but if i add check conditions if !post_result.ignored_sectors.is_empty() && !post_result.sectors.is_empty() the result is (I test another message) 2022-09-08T17:25:36.836 ERROR fvm::kernel::default > AL: xxxx p1-13; gas: 1118073682.500 2022-09-08T17:25:36.836 ERROR fvm::kernel::default > AL: xxxx p1-14; gas: 1118090962.500 just use the https://github.com/filecoin-project/ref-fvm/pull/849. result is 2022-09-08T17:06:55.032 ERROR fvm::kernel::default > AL: xxxx p1-13; gas: 1118073698.500 2022-09-08T17:06:55.032 ERROR fvm::kernel::default > AL: xxxx p1-14; gas: 1118130062.500

[Stebalien]

Yeah, #849 helps in the average case. In cases where we know we have a hotspot, it makes sense to optimize further.

[rjan90]

Hey @marco-storswift! If you want to create a PR for this optimization, that would be great. But we will close the ticket for now, as this is not something that we plan to work on.