CORESCHED(1)

💖 CORESCHED 💖

okay bestie, welcome to coresched — the User Commands girlie whose whole entire job is managing core scheduling cookies for tasks. yes it's real, yes it's a whole vibe, let's get into it 🍪✨

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🌸 NAME 🌸

coresched — manage core scheduling cookies for tasks

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✨ SYNOPSIS ✨

coresched [get] [-s pid]

coresched new [-t type] -d pid

coresched new [-t type] -- command [argument...]

coresched copy [-s pid] [-t type] -d pid

coresched copy [-s pid] [-t type] -- command [argument...]

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🦋 DESCRIPTION 🦋

So. The coresched command is literally here to retrieve or modify the core scheduling cookies of a running process — you give it a pid, it does its thing. Or! It can spawn a brand new command with core scheduling cookies already attached. main character entrance fr fr 💅

Now what even is core scheduling, you ask? Okay so: it permits the definition of groups of tasks that are allowed to share a physical core. How? By assigning a cookie to each task. And the rule is — only tasks that have the same cookie are allowed to be scheduled on the same physical core. no cookie match, no sharing, periodt.

Two options for the cookie situation:

• assign a new random cookie to a task, OR
• copy a cookie from another task.

And that's it. It is not possible to choose the value of the cookie. nope. not yours to pick. the kernel decides, you just vibe 😌

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🎀 FUNCTIONS 🎀

get

Retrieve the core scheduling cookie of the PID you put in -s. And if you just... don't include -s? It'll get the cookie of the current coresched process itself. self-love honestly 🫶

new

Assign a new cookie to an existing PID specified in -d, or execute command with a new cookie. fresh start energy ✨

copy

Copy the cookie from an existing PID (-s) to another PID (-d), or execute command with that cookie. And if -s is omitted? It gets the cookie of the current coresched process. again. self-copy, iconic 🎀

Also: if you specify no function at all, it will just run the get function. default behaviour, no notes 💅

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👑 OPTIONS 👑

• -s, --source PID — which PID to get the cookie from. If this option is omitted, it will get the cookie from the current coresched process. (yes, again. it's a theme.)
• -d, --dest PID — which PID to modify the cookie of. this is the glow-up target 🌈
• -t, --dest-type TYPE — the type of the PID whose cookie will be modified. And it can be one of three values:
  • pid, or process ID
  • tgid, or thread group ID (default value) ⭐
  • pgid, or process group ID
• -v, --verbose — show extra information when modifying cookies of tasks. the girlies love a little extra detail 💜
• -h, --help — display help text and exit. we love a quick escape 🙈
• -V, --version — display version and exit.

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🔥 EXAMPLES 🔥

Get the core scheduling cookie of the coresched task itself, usually inherited from its parent:

coresched get

Get the core scheduling cookie of a task with PID 123:

coresched get -s 123

Give a task with PID 123 a new core scheduling cookie:

coresched new -d 123

Spawn a new task with a new core scheduling cookie:

coresched new -- command [argument...]

Copy the cookie from the current coresched process to another task with pid 456:

coresched copy -d 456

Copy the cookie from a task with pid 123 to another task with pid 456:

coresched copy -s 123 -d 456

Copy the cookie from a task with pid 123 to a new task command:

coresched copy -s 123 -- command [argument...]

Copy the cookie from a task with pid 123 to the process group ID 456:

coresched copy -s 123 -t pgid -d 456

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🧚 PERMISSIONS 🧚

Okay so this part is not optional, bestie. Retrieving or modifying the core scheduling cookie of a process requires PTRACE_MODE_READ_REALCREDS ptrace access to that process. And for the full lore on that, see the section "Ptrace access mode checking" in ptrace(2). iykyk 😭

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⭐ EXIT STATUS ⭐

On success, coresched returns 0. If coresched fails, it will print an error and return 1. no cap.

But — if a command is being executed, the return value of coresched will be the return value of command. so like. the command is the one holding the mic at that point 🎤

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💀 NOTES 💀

coresched requires core scheduling support in the kernel. This can be enabled via the CONFIG_SCHED_CORE kernel config option. no kernel support, no cookies, no slay. period.

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💜 AUTHORS 💜

Thijs Raymakers <thijs@raymakers.nl>, Phil Auld <pauld@redhat.com>

the icons who built this. we thank them 🫶

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🌸 COPYRIGHT 🌸

Copyright © 2024 Thijs Raymakers and Phil Auld. This is free software licensed under the EUPL.

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🎀 SEE ALSO 🎀

chrt(1), nice(1), renice(1), taskset(1), ptrace(2), sched(7)

Also — the Linux kernel source files:

Documentation/admin-guide/hw-vuln/core-scheduling.rst

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🐛 REPORTING BUGS 🐛

For bug reports, use the issue tracker <https://github.com/util-linux/util-linux/issues>.

please actually report them and not just complain in the group chat bestie, i'm begging 🙈

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🌈 AVAILABILITY 🌈

The coresched command is part of the util-linux package, which can be downloaded from the Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.

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and that's the whole page, angel 💖 this was util-linux 2.42.4, dated 2026-09-21, and yes that date is lowkey in the future, we don't ask questions, we just say slay. go forth and sort your cookies 🍪💅✨