EEVDF, sched-ext, ECHO and RT Scheduler

1️⃣ EEVDF (Earliest Eligible Virtual Deadline First)

Status: Upstream Linux default (since Linux 6.6)

What it is

EEVDF is the modern replacement for CFS (Completely Fair Scheduler). It is a deadline-based scheduler designed to improve fairness, latency, and interactivity.

Instead of “who ran least recently?”, it asks:

Who has the earliest virtual deadline and is eligible to run now?

Why it exists

CFS struggled with:

• Bursty interactive workloads
• Low-latency desktop responsiveness
• Edge cases with fairness under mixed loads

EEVDF fixes these while remaining fully fair and general-purpose.

Key characteristics

• ⚖️ Strict fairness guarantees
• ⚡ Lower scheduling latency than CFS
• 🧠 Better handling of interactive bursts (UI, browsers, games)
• 🔄 Fully upstream and well-tested

How it feels in practice

• Smooth desktop
• Consistent frame pacing
• No surprises under load

Best for

✅ General desktop use ✅ Gaming + background tasks ✅ Coding, compiling, browsing simultaneously

👉 If you want “it just works”, this is the safe baseline.

2️⃣ sched-ext (Scheduler Extensions)

Status: Experimental but upstream framework

What it is

sched-ext is not a scheduler, but a framework that allows user-space schedulers written in BPF to control task scheduling.

Think of it as:

“Pluggable scheduling logic without recompiling the kernel.”

Why it exists

Kernel scheduling experimentation is:

• Hard
• Slow
• Risky

sched-ext allows:

• Rapid prototyping
• Custom schedulers per workload
• Research & experimentation

Key characteristics

• 🧩 User-space defined scheduling logic
• 🔬 Ideal for experimentation
• ⚠️ Can be unstable depending on the scheduler used
• 🧠 Extremely flexible

How it feels in practice

• Depends entirely on the scheduler plugged in
• Can be amazing or terrible
• Debugging requires expertise

Best for

✅ Scheduler developers ✅ Researchers ✅ Power users experimenting with custom policies

❌ Not ideal for daily gaming or productivity (yet)

3️⃣ ECHO Scheduler

Status: Out-of-tree / niche (CachyOS custom)

What it is

ECHO is a latency-oriented scheduler designed for:

• Fast wake-ups
• Minimal overhead
• Desktop responsiveness

It prioritizes:

• Recently interactive tasks
• UI-related workloads
• Short CPU bursts

Design philosophy

“Responsiveness first, fairness second.”

Unlike EEVDF:

• Less strict fairness
• More aggressive prioritization of interactive tasks

Key characteristics

• ⚡ Very snappy UI
• 🎮 Good for gaming input latency
• 📉 Can reduce throughput fairness under heavy load
• 🧪 Less tested than EEVDF

How it feels in practice

• Very “light”
• UI reacts instantly
• Heavy background jobs may feel deprioritized

Best for

✅ Gaming-focused systems ✅ Minimal background workloads ✅ Low-latency desktop feel

❌ Not ideal if you compile kernels while gaming

4️⃣ RT (Real-Time Scheduler)

Status: Linux core (SCHED_FIFO / SCHED_RR)

What it is

RT scheduling is hard priority scheduling:

• RT tasks always preempt normal tasks
• No fairness guarantees
• Can lock up your system if misused

Types

• SCHED_FIFO – runs until it blocks or yields
• SCHED_RR – round-robin among RT tasks

Key characteristics

• 🚨 Absolute priority
• ⛔ Can starve the system
• 🎯 Deterministic timing

How it feels in practice

• Used by:

  • Audio engines (JACK, PipeWire RT threads)
  • Industrial control
  • Robotics

Best for

✅ Audio production ✅ Hard real-time requirements

❌ Never use as a general desktop scheduler

🔎 Quick Comparison

🧠 Practical Advice for Your Setup (CachyOS + Hyprland + RTX 3080)

• EEVDF → Best balance for gaming + coding
• ECHO → Try if you want maximum snappiness and minimal background load
• sched-ext → Only if you enjoy kernel experimentation
• RT → Leave it alone unless doing audio or robotics