The next Linux kernel development cycle—expected to become Linux 6.20, or more likely Linux 7.0—is shaping up to deliver a meaningful improvement to io_uring, specifically around how IOPOLL polling is handled.
It’s not the kind of change that grabs headlines. But for workloads that lean heavily on asynchronous I/O, it’s exactly the sort of fix that quietly removes long-standing inefficiencies.
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What’s Changing in io_uring IOPOLL
Jens Axboe, io_uring’s lead developer and Linux block maintainer, has queued a patch into the for-7.0/io_uring branch that reworks how IOPOLL requests are tracked internally.
Until now, io_uring has managed issued and pending IOPOLL read/write requests using a singly linked list. That design comes with a subtle but real limitation:
- Individual requests can’t be removed easily
- A request at position N can only be completed if all requests from 0 to N-1 are also complete
As Axboe explains, this behavior isn’t necessarily problematic for homogeneous I/O workloads, where operations complete in roughly the same order.
But once you introduce:
- Multiple devices being polled in the same ring, or
- Different types of I/O with uneven completion times,
the model starts to fall apart. Completed requests can sit around waiting, even though there’s no technical reason they couldn’t be finalized immediately.
In other words, completion is artificially delayed, not because the I/O isn’t done—but because the data structure says “not yet.”
The Fix: A Doubly Linked List
The proposed solution is straightforward, but impactful.
Instead of a singly linked list, io_uring will now track IOPOLL completions using a doubly linked list. That small internal change makes it possible to:
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- Remove individual completed requests cleanly
- Complete whichever I/O operations have actually finished
- Avoid unnecessary head-of-line blocking
As Axboe put it, this allows io_uring to “easily complete whatever requests were polled done successfully,” rather than forcing everything to wait in order.
Why This Matters to Real Workloads
This isn’t just a theoretical cleanup.
Fengnan Chang from Bytedance originally posted the patch and shared benchmark results showing measurable performance improvements in polling mode workloads. While the gains won’t matter to every application, they’re especially relevant for:
- High-throughput storage systems
- Mixed-device I/O environments
- Latency-sensitive async I/O users already pushing io_uring hard
For these cases, shaving off avoidable delays in request completion directly translates into better throughput and more predictable latency.
A Small Change, the Right Kind of Progress
This patch is a good example of how io_uring continues to mature.
There’s no flashy new API here, no behavioral changes developers need to adapt to—just a smarter internal structure that aligns better with how modern I/O workloads actually behave.
Assuming it lands as expected, Linux 6.20—or whatever ultimately becomes Linux 7.0—will quietly deliver yet another reason io_uring remains one of the kernel’s most important subsystems for modern Linux I/O.
Sometimes, the most valuable performance improvements are the ones you don’t notice—because the system simply stops getting in its own way.
