..
 # Copyright (c) 2026, Arm Limited.
 #
 # SPDX-License-Identifier: MIT

##################
Regression Tracker
##################

************
Introduction
************

Fastpath monitors the Linux kernel across a range of hardware platforms and
workloads. When a statistically significant performance change is detected
between two kernel versions, it is raised as a tracked regression entry and
investigated. This page records all known findings together with their current
status and, where available, links to upstream reports and fix commits.

**Column descriptions:**

- **ID** – Tracking identifier (e.g. ``FP-619-02``).
- **Branch / Good / Bad** – The kernel tree and the two versions that bracket
  the regression.
- **SUT(s)** – System(s) Under Test on which the regression was observed.
- **Benchmark / Resultclass** – The specific workload and measured quantity.
- **Delta** – Measured change between the good and bad kernel versions.
- **Regressing Commit** – The first bad commit identified by bisection.
- **Status** – One of four states:

  - *Detected* – Regression observed; queued for investigation.
  - *Investigating* – Currently under active investigation.
  - *Reported* – Reported upstream; awaiting a fix.
  - *Fixed* – Fix merged upstream.

- **Report** – Link to the upstream mailing-list report or patch.
- **Fix Commit(s)** – Commit(s) that resolved the regression.

********************
Regression History
********************

.. list-table::
   :header-rows: 1
   :widths: 8 8 10 16 22 24 7 18 10 16 18

   * - ID
     - Branch
     - Good Kernel
     - Bad Kernel
     - SUT(s)
     - Benchmark / Resultclass
     - Delta
     - Regressing Commit
     - Status
     - Report
     - Fix Commit(s)

   * - FP-614-01
     - mainline
     - 6-13-0
     - 6-14-0-rc4
     - aws-m7g.metal-01
     - mmtests/hackbench

       (process-pipes-30)
     - -10.69%
     - ``aaec5a95d596``

       *"pipe_read: don't wake up the writer if the pipe is still full"*
     - Fixed
     - `Upstream report <https://lore.kernel.org/all/3170d16e-eb67-4db8-a327-eb8188397fdb@amd.com/>`__
     -

   * - FP-615-01
     - mainline
     - 6-15-0-rc1
     - 6-15-0-rc2
     - aws-m7g.metal-01
     - pts/pgbench

       Scale: 100 Clients: 1000, Read Only (TPS)
     - -98.81%
     - ``7ab4f0e37a0f``

       *"ACPI PPTT: Fix coding mistakes in a couple of sizeof() calls"*
     - Fixed
     - `Upstream report <https://lore.kernel.org/all/20250514130727.67734-1-aishwarya.tcv@arm.com/>`__
     - ``adfab6b39202``

       *"ACPI: PPTT: Fix processor subtable walk"*

   * - FP-619-01
     - mainline
     - 6-18-0
     - 6-19-0-rc1
     - aws-m7g.metal-01
     - micromm/vmalloc

       fix_align_alloc_test: p:1, h:0, l:500000 (usec)
     - -40.57%
     - ``a06157804399``

       *"mm/vmalloc: request large order pages from buddy allocator"*
     - Reported
     - `Upstream report <https://lore.kernel.org/all/66919a28-bc81-49c9-b68f-dd7c73395a0d@arm.com/>`__
     -

   * - FP-619-02
     - mainline
     - 6-18-0
     - 6-19-0-rc1
     - aws-m7g.metal-01

       cesw-aarch64-ampereone-1s-a192-32x-02
     - schbench/thread-contention

       (-m 64 -t 4 -r 10 -s 1000), avg_rps (req/sec)
     - -17.41%
     - ``e837456fdca8``

       *"sched/fair: Reimplement NEXT_BUDDY to align with EEVDF goals"*
     - Fixed
     - `Upstream report <https://lore.kernel.org/all/4b96909a-f1ac-49eb-b814-97b8adda6229@arm.com/>`__
     - ``4f70f106bca1``

       *"sched/fair: Disable scheduler feature NEXT_BUDDY"*

       ``15257cc2f905``

       *"sched/fair: Revert force wakeup preemption"*

       *(merged in 6-19-0-rc7)*

   * - FP-619-03
     - mainline
     - 6-18-0
     - 6-19-0-rc2
     - aws-m7g.metal-01
     - micromm/munmap

       p:1, d:10 (seconds)
     - -23.74%
     - ``7e44d00a13ca``

       *"memcg: use mod_node_page_state to update stats"*
     - Reported
     - `Upstream report <https://lore.kernel.org/all/1052a452-9ba3-4da7-be47-7d27d27b3d1d@arm.com/>`__
     -

   * - FP-700-01
     - mainline
     - 6-19-0
     - 7-0-0-rc1
     - aws-m7i.24xlarge-01

       aws-m7g.metal-01

       cesw-aarch64-ampereone-1s-a192-32x-02
     - micromm/vmalloc

       kvfree_rcu_2_arg_vmalloc_test: p:1, h:0, l:500000 (usec)
     - -9.26%
     - ``e47c897a2949``

       *"slab: add sheaves to most caches"*
     - Investigating
     -
     -