4 ms·

Well, for the two examples I named: vm.swappiness defaults to 60, which is default from when everyone was still running spinning rust with a swap partition. Se

by jorvi 11mo ago

Well, for the two examples I named: vm.swappiness defaults to 60, which is default from when everyone was still running spinning rust with a swap partition. Servers these days usually have very specific storage+memory configurations, whereas the usual desktop or laptop has an SSD and 16GB+ of RAM with RAM compression expanding it. Lazy RCU loading is good on a laptop because you only lose about 10% performance and only with specific workloads, but your idle and light load energy consumption improves. Most laptops spend like 95%+ in light or idle load scenarios. Conversely, on a desktop you don't care (much) about idle and light load energy consumption, you only care about keeping max load consumption low enough so that your fans stay quiet. And on a workstation you don't care about a system being whisper quiet so you can go nuts with the energy consumption.

malwrar 11mo ago
I totally missed that part of your comment, my bad. Thanks for elaborating on those, I feel inspired to experiment! So far my kernel journey has been about making my hardware work + enabling features, and that’s mostly how I’ve been discovering config options. Do you have any suggestions on where one aught to read further on this sort of kernel tuning? EDIT: doing some further research, couldn’t you just set those options via sysctl w/o needing to build a separate kernel?
- jorvi 11mo ago
  Yes you can adjust them via sysctl or directly as kernel parameter arguments. That isn't my point. My point is that Linux has some horrible defaults :+)
  - malwrar 11mo ago
    Makes sense! Thanks for turning me on to them, I hadn’t come across those yet in my journey.
johnny22 11mo ago
Swappiness and many others can be changed by some sort of system preset rather built that way. I know not ALL options can be done that way, but I'd want to see changes start there where feasible.
prmoustache 11mo ago
> vm.swappiness defaults to 60, which is default from when everyone was still running spinning rust with a swap partition. Servers these days usually have very specific storage+memory configurations, whereas the usual desktop or laptop has an SSD and 16GB+ of RAM with RAM compression expanding it. You don't need to compile a specific kernel for that, this is setup via sysctl.
jcalvinowens 11mo ago
> Lazy RCU loading is good on a laptop Do you mean RCU_LAZY? Most distros will already enable that: it doesn't do anything without rcu_nocbs, so there's no negative impact on server workloads. [calvin@debian-trixie ~] grep RCU_LAZY /boot/config-6.12.57+deb13-amd64 CONFIG_RCU_LAZY=y # CONFIG_RCU_LAZY_DEFAULT_OFF is not set [calvin@debian-trixie ~] grep RCU_NOCB_CPU /boot/config-6.12.57+deb13-amd64 CONFIG_RCU_NOCB_CPU=y # CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/rcu/tree.c#n3129 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... You just have to set rcu_nocbs on the kernel cmdline.

by jorvi 11mo ago

malwrar 11mo ago

I totally missed that part of your comment, my bad. Thanks for elaborating on those, I feel inspired to experiment! So far my kernel journey has been about making my hardware work + enabling features, and that’s mostly how I’ve been discovering config options. Do you have any suggestions on where one aught to read further on this sort of kernel tuning? EDIT: doing some further research, couldn’t you just set those options via sysctl w/o needing to build a separate kernel?

jorvi 11mo ago
Yes you can adjust them via sysctl or directly as kernel parameter arguments. That isn't my point. My point is that Linux has some horrible defaults :+)
- malwrar 11mo ago
  Makes sense! Thanks for turning me on to them, I hadn’t come across those yet in my journey.

johnny22 11mo ago

Swappiness and many others can be changed by some sort of system preset rather built that way. I know not ALL options can be done that way, but I'd want to see changes start there where feasible.

prmoustache 11mo ago

> vm.swappiness defaults to 60, which is default from when everyone was still running spinning rust with a swap partition. Servers these days usually have very specific storage+memory configurations, whereas the usual desktop or laptop has an SSD and 16GB+ of RAM with RAM compression expanding it. You don't need to compile a specific kernel for that, this is setup via sysctl.

jcalvinowens 11mo ago

> Lazy RCU loading is good on a laptop Do you mean RCU_LAZY? Most distros will already enable that: it doesn't do anything without rcu_nocbs, so there's no negative impact on server workloads. [calvin@debian-trixie ~] grep RCU_LAZY /boot/config-6.12.57+deb13-amd64 CONFIG_RCU_LAZY=y # CONFIG_RCU_LAZY_DEFAULT_OFF is not set [calvin@debian-trixie ~] grep RCU_NOCB_CPU /boot/config-6.12.57+deb13-amd64 CONFIG_RCU_NOCB_CPU=y # CONFIG_RCU_NOCB_CPU_DEFAULT_ALL is not set https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/rcu/tree.c#n3129 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin... You just have to set rcu_nocbs on the kernel cmdline.