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Avoid overhead from dynamic calls about async_bench HOT 5 OPEN

xiangpenghao commented on June 17, 2024

Avoid overhead from dynamic calls

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XiangpengHao commented on June 17, 2024

Hi @lachlansneff, thanks for your suggestions!

The Box<dyn Future<Output = u64> + 'inner> does issue two allocations, but only on task creation (https://github.com/XiangpengHao/async_bench/blob/master/src/executor.rs#L22), which in our case only happens const times (i.e. 4 times)

I tried the nightly version, the performance improved around 30% in our case.

I'm also wondering if we can reuse futures to reduce runtime allocation to zero...

Please let me know if my understanding is incorrect, I'm new to rust :)

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lachlansneff commented on June 17, 2024

Your assumptions here are a little bit wrong. `Box<dyn Future<Output = u64> + ‘inner>` allocates once. And even though the allocations only occur once per task, there’s still actually a _lot_ of overhead from having to poll a dynamic future. Having the futures be a concrete type that can get inlined will reduce overhead a lot.

…

On Wed, Jul 15, 2020 at 7:34 PM Xiangpeng Hao ***@***.***> wrote: Hi @lachlansneff <https://github.com/lachlansneff>, thanks for your suggestions! The Box<dyn Future<Output = u64> + 'inner> does issue two allocations, but only on task creation ( https://github.com/XiangpengHao/async_bench/blob/master/src/executor.rs#L22), which in our case only happens const times (i.e. 4 times) I tried the nightly version, the performance improved around 30% in our case. I'm also wondering if we can reuse futures to reduce runtime allocation to zero... Please let me know if my understanding is incorrect, I'm new to rust :) — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHPIOK7F5UK3HAUXELCZL33R3Y4GTANCNFSM4OWZWTMA> .

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XiangpengHao commented on June 17, 2024

Oh yes, the poll will need to dereference the pointer, which can be costly.
Thanks! I'm trying the async-task crate to see if I can do this easily.

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lachlansneff commented on June 17, 2024

It’s actually not that the dereference is expensive, it’s that calling a function on a dynamic trait requires an actual call, which is expensive (in comparison to what we’re doing here). So you want to give the compiler enough information to inline `poll`. I wrote an example on the rust playground a week or so ago to act as an example: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=3ddca1f690fd61d069e14d1d5f5d9fce

…

On Thu, Jul 16, 2020 at 12:49 PM Xiangpeng Hao ***@***.***> wrote: Oh yes, the poll will need to dereference the pointer, which can be costly. Thanks! I'm trying the async-task crate to see if I can do this easily. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHPIOK4WUEPHRU7KWUBFVCTR34VSRANCNFSM4OWZWTMA> .

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XiangpengHao commented on June 17, 2024

Oh cool, I see. I didn't know we can write code like that :-) Thanks for letting know!

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Avoid overhead from dynamic calls about async_bench HOT 5 OPEN

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