SCHED_4BSD(4)

💖 sched_4bsd — the 4.4BSD scheduler 💖

okay bestie, so this is sched_4bsd(4), straight out of the Kernel Interfaces Manual — it's the og scheduler and she's been here forever, no cap. sit down, drink your strawberry milk, we're gonna talk about how your kernel decides who runs. 🍓✨

🌸 SYNOPSIS 🌸

options SCHED_4BSD

that's it. that's the whole vibe check. 💅

🦋 DESCRIPTION 🦋

So sched_4bsd is the traditional system scheduler, and honestly? she serves. She gives you both high throughput and solid interactive response, even when the system is under load. like, she's been doing this since before you were born and she has not lost a step. 👑

The following sysctls are relevant to how sched_4bsd operates, and you're gonna want to know all of them:

• kern.sched.name — read-only, bestie, look don't touch 🙈. This one reports the name of the active scheduler. Just telling you who's on duty.
• kern.sched.quantum — read-write, so you can play with this one. It reports or sets the length of the quantum (measured in micro-seconds) that gets granted to a thread. That's how long a thread gets to be the main character before she has to share the aux. 🎀
• kern.sched.ipiwakeup.enabled — also read-write! This one sets whether or not the scheduler will generate an inter-processor interrupt (IPI) to an idle CPU when a thread is woken up. If you turn it off, those idle CPUs just… wait. They sit there until the next clock tick before they even start looking for new work. ngl that's giving sleepy energy 😴 but it's your call.
• kern.sched.preemption — read-only again! It reports whether or not the kernel is configured to support preemption, which reduces the latency to run lower priority threads on wakeup. Fancy. ✨

Heads up bestie: some of these sysctls will only be available on systems that support SMP. If your machine doesn't have it, don't come crying to me, the sysctl just won't be there. 😭

🌈 SEE ALSO 🌈

• sched_ule(4)
• sysctl(8)

go read those too, i'll wait. 🫶

👑 HISTORY 👑

The sched_4bsd scheduler has been present, in various forms, since the inception of BSD. like literally the beginning. she's an icon, she's a legend, and she is the moment. ⭐

💀 BUGS 💀

Okay so real talk — sched_4bsd is a highly robust and time-tested scheduler, periodt. BUT. She lacks specific knowledge of how to schedule advantageously in non-symmetric processor configurations, such as hyper-threading. So if your CPU is out here with that asymmetric setup, she doesn't really know how to play it to her advantage. not her fault, she's just built different (literally). 😔

mwah 💜 that's the whole page, bestie. this one came from the Debian folks, dated January 21, 2008 — yeah, she's vintage, and vintage is always in. 🎀✨ bye bye! 🦋