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Increasing the queue size to handle container storage workloads #177

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HuijingHei wants to merge 1 commit into from
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Increasing the queue size to handle container storage workloads #177

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2 changes: 1 addition & 1 deletion crates/kit/src/libvirt/domain.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -465,7 +465,7 @@ impl DomainBuilder {
"filesystem",
&[("type", "mount"), ("accessmode", "passthrough")],
)?;
writer.write_empty_element("driver", &[("type", "virtiofs"), ("queue", "1024")])?;
writer.write_empty_element("driver", &[("type", "virtiofs"), ("queue", "4096")])?;
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@gemini-code-assist gemini-code-assist bot Dec 17, 2025

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medium

The virtiofs queue size 4096 is a magic number. To improve readability and maintainability, it's best to define this as a constant. This also makes it easier to update in the future and to reference from tests.

The tests in test_virtiofs_filesystem_configuration are currently failing because they still assert the old queue size of 1024. Using a constant would help resolve this and prevent it from happening in the future.

You can add the following constant at the top of the file:

const VIRTIOFS_QUEUE_SIZE: &str = "4096";

Then, use this constant here and in the tests.

Suggested change
writer.write_empty_element("driver", &[("type", "virtiofs"), ("queue", "4096")])?;
writer.write_empty_element("driver", &[("type", "virtiofs"), ("queue", VIRTIOFS_QUEUE_SIZE)])?

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@cgwalters cgwalters Dec 17, 2025

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I don't have any theory offhand why increasing the queue size here would make a difference - unless it somehow could relate to the maximum number of fds?

Either way it's probably useful to have an explicit rationale for why we picked the number. A reference to another virt framework (libvirt or systemd-vmspawn) could make sense here.

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@HuijingHei HuijingHei Dec 18, 2025

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I don't have any theory offhand why increasing the queue size here would make a difference - unless it somehow could relate to the maximum number of fds?

The change was proposed by AI, and I meant want to give it a try, though I do not sure about this.

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@HuijingHei HuijingHei Dec 18, 2025

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Thank you! Looks this is not great to set to 4096, will close this and find another workaround.

Potential upside
Slight improvement only if:

- Very high parallel fs ops
- Many vCPUs (≥16–32)
- Heavy metadata churn (massive parallel builds, stress tests)

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@cgwalters cgwalters Dec 18, 2025

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The change was proposed by AI,

That's fine, though why was this commit missing the attribution?
https://github.com/bootc-dev/infra/blob/2dd498656b9653c321e5d9a8600e6b506714acb3/common/AGENTS.md#attribution

Not a big deal, but it's really helpful to know in general when one is looking at something a human thought vs something that came from AI or a hybrid.

if filesystem.readonly {
writer.write_empty_element("readonly", &[])?;
}
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