[Deepin-Kernel-SIG] [linux 6.6.y] [deepin] Input: evdev - Modify the process of closing the evdev device to use …

[opsiff]

…the synchronize_rcu_expedited interface to speed up the shutdown process.

deepin inclusion
categroy: performace

As Documentations saied:
synchronize_rcu_expedited() instead
of synchronize_rcu(). This reduces latency,
but can increase CPU utilization, degrade
real-time latency, and degrade energy efficiency.
use it to optimize the shutdown process by
our system developer report where some input dev shutdown cost many XXms.
With the patched kernel, shutdown cost time from 5.96 to 5.11.

Tested-by: qiancheng qiancheng@uniontech.com

Summary by Sourcery

Enhancements:

• Conditionally use synchronize_rcu_expedited() instead of synchronize_rcu() during evdev client cleanup when the system is halting, powering off, or restarting to reduce shutdown latency.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR adjusts the evdev client detach path to use synchronize_rcu_expedited() instead of synchronize_rcu() during system halt, power-off, or restart, in order to reduce shutdown latency while preserving the normal synchronize_rcu() behavior in all other runtime cases.

Sequence diagram for evdev_detach_client RCU synchronization on shutdown

sequenceDiagram
    participant Caller
    participant evdev as evdev_detach_client
    participant RCU as RCU_subsystem
    Caller->>evdev: evdev_detach_client(evdev, client)
    evdev->>evdev: spin_lock(evdev->client_lock)
    evdev->>evdev: list_del_rcu(client->node)
    evdev->>evdev: spin_unlock(evdev->client_lock)
    alt system_state is SYSTEM_HALT or SYSTEM_POWER_OFF or SYSTEM_RESTART
        evdev->>RCU: synchronize_rcu_expedited()
        RCU-->>evdev: expedited grace period complete
    else system_state is any other state
        evdev->>RCU: synchronize_rcu()
        RCU-->>evdev: normal grace period complete
    end
    evdev-->>Caller: detach complete

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Flow diagram for conditional RCU synchronization in evdev_detach_client

flowchart TD
    A["Start evdev_detach_client"] --> B["Acquire client_lock spinlock"]
    B --> C["Remove client from list with list_del_rcu"]
    C --> D["Release client_lock spinlock"]
    D --> E{system_state}
    E -->|SYSTEM_HALT| F["Call synchronize_rcu_expedited"]
    E -->|SYSTEM_POWER_OFF| F
    E -->|SYSTEM_RESTART| F
    E -->|Any other state| G["Call synchronize_rcu"]
    F --> H["RCU grace period completed"]
    G --> H
    H --> I["Return from evdev_detach_client"]

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File-Level Changes

Change	Details	Files
Optimize evdev client-detach RCU grace-period waiting during system shutdown sequences to reduce input device shutdown latency.	Replace the unconditional synchronize_rcu() call after removing an evdev client from the RCU list with a conditional that checks the global system_state. Invoke synchronize_rcu_expedited() when system_state indicates SYSTEM_HALT, SYSTEM_POWER_OFF, or SYSTEM_RESTART to shorten the grace period during shutdown. Fallback to the original synchronize_rcu() behavior when the system is in any other state to avoid the higher CPU/latency overhead of expedited RCU in normal operation.	drivers/input/evdev.c

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[sourcery-ai]

Hey - I've left some high level feedback:

• The repeated system_state checks can be simplified by using an existing helper like in_shutdown() (if available in this kernel) or a small static inline helper, which will make the intent clearer and reduce duplication.
• Given the higher cost of synchronize_rcu_expedited(), it would be worth briefly confirming that evdev_detach_client() is only called a small, bounded number of times during shutdown so this change doesn’t introduce unnecessary CPU spikes in that path.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The repeated `system_state` checks can be simplified by using an existing helper like `in_shutdown()` (if available in this kernel) or a small static inline helper, which will make the intent clearer and reduce duplication.
- Given the higher cost of `synchronize_rcu_expedited()`, it would be worth briefly confirming that `evdev_detach_client()` is only called a small, bounded number of times during shutdown so this change doesn’t introduce unnecessary CPU spikes in that path.

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[Copilot]

Pull request overview

This PR optimizes evdev client teardown during system shutdown by switching from a normal RCU grace-period wait to an expedited one when the kernel is halting, powering off, or restarting, reducing shutdown latency in the input stack.

Changes:

• Update evdev_detach_client() to call synchronize_rcu_expedited() when system_state is SYSTEM_HALT, SYSTEM_POWER_OFF, or SYSTEM_RESTART.
• Preserve existing behavior (synchronize_rcu()) during normal runtime.

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