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speed up BIOS bootloader by Freax13 · Pull Request #550 · rust-osdev/bootloader · GitHub

/ bootloader Public

speed up BIOS bootloader - #550

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Freax13 merged 2 commits into
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enhancement/bios-disk-speed
Mar 18, 2026
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speed up BIOS bootloader#550
Freax13 merged 2 commits into
mainfrom
enhancement/bios-disk-speed

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Freax13 commented Mar 18, 2026 •
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This PR speeds up the BIOS bootloader by reducing the number of disk read operations. See commits for details.

This reduces the runtime of the large_ramdisk test (with KVM enabled) from ~35s to ~9s.

Closes #549

Freax13 added 2 commits March 18, 2026 07:51
merge reads for contiguous clusters
0ab866d 
Doing many small reads is much slower than doing fewer large reads.
Let's try to read several clusters at once if they're contiguous.
skip reads if the data is already buffered
65f5385 
read_exact_at is often called with a bunch of offsets in the same
general area. In a lot of cases, the data needed is still in the
buffer from the last call. Let's make use of that by remembering the
last sector read and skip reading the same sector again.

Freax13 commented Mar 18, 2026

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@NikoPit please check if that resolves your issue.

phil-opp approved these changes Mar 18, 2026
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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

Thanks a lot!

NikoPit commented Mar 18, 2026

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yup it significently sped up the boot time, thanks

NikoPit mentioned this pull request Mar 18, 2026
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NikoPit commented Mar 18, 2026

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tho its still pretty slow, but this definitely made it a lot more better

NikoPit commented Mar 18, 2026

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btw completely off topic, is there a discord server specificly for this?

Freax13 merged commit 48b9311 into main Mar 18, 2026
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Freax13 commented Mar 18, 2026

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tho its still pretty slow, but this definitely made it a lot more better

It's about as fast as the UEFI implementation. I think at some point you just have to accept that loading large files is going to take some time 😅

btw completely off topic, is there a discord server specificly for this?

No, but there's a Zulip.

phil-opp mentioned this pull request Jul 7, 2026
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Loading the ramdisk takes an insanely long time

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