optimized kernel + disabled ohmd cgroup plugin = better reactions, less lagging

[stano]

hi

after playing with some options in my self compiled kernel
i found that disabling CONFIG_PREEMPT and set CONFIG_SLAB instead of CONFIG_SLUB make phone less lagging and playing with phone is more enjoyable.

if you dont know how to compile your own kernel, you can use mine, but i dont have .deb and i will not make .deb package
http://blackhole.sk/~stanojr/n900/
1. untar 2.6.28.10-maemo-omap1.tar.gz in /lib/modules/
2. run depmod 2.6.28.10-maemo-omap1
3. flash zImage via usb cable
(in your pc run flasher-3.5 -k zImage -f -R)
4.enjoy

if phone dont boot, flash original nokia kernel, original modules are not removed, so it must boot without problem.

my kernel is based on kernel-maemo12 from extras-devel with 2.6.28.10 patch from http://natisbad.org/N900/n900-custom-kernel.html + 1900 - * - 1925 patches from http://dev.gentoo.org/~dsd/genpatches/trunk/2.6.28/

bonus: i add ramzswap.ko from compcache-6.2, so you can play with ramzswap

and i forgot, i changed default I/O scheduler from cfq to deadline

---

you can get another speed by disabling cgroup plugin in ohmd.

what is cgroup and for what is used ?
ohmd daemon use cgroup to set different policy to new executed process.
you can look at this config file and everything will be more clear:
/usr/share/policy/etc/current/syspart.conf

cgroup feature (mounted in /syspart) is used to limit group of processes running in linux. in n900 divided to applications and desktop. it set different cpu-share (cpu scheduler) and limit memory per groups.
when enabled after executing new process ohmd will assign new process to specified group.
it causes overhead.
i dont need this feature, you do ?


how to disable it ?
1.mv /usr/lib/ohm/libohm_cgroups.so /usr/lib/ohm/libohm_cgroups.so.disabled
2. reboot your phone
ohmd will start but without cgroup module, /syspart/ will not be mounted and desktop reactions are faster and every process have same cpu-share. just like in normal linux desktop like in ubuntu/debian/...
3. enjoy

[jacktanner]

This is interesting, but is there any way to get some objective numbers on the difference in performance? And to only try one change at a time?

[Tomaszd]

On a related note, has anyone tried using BFS with the stock kernel? Seems it would a perfect fit. I can't link to Wikipedia, as even the URL filters on the "F" word. Here's source http://ck.kolivas.org/patches/bfs/

[SavageD]

has anyone tried this? this may actually help the emulators o.o

[soeiro]

Hummm, that's interesting. One would think that enabling CONFIG_PREEMPT would increase responsiveness, not disabling it (it comes enabled in the default N900 config).

@stano: Where do you see reduction of lags?

[iKneaDough]

Originally Posted by stano

bonus: i add ramzswap.ko from compcache-6.2, so you can play with ramzswap

were you also able to successfully apply the kernel patch for the swap free notify callback?

also any plans for adding undervolting and overclocking to your kernels?

[tokag]

Originally Posted by stano

how to disable it ?
1.mv /usr/lib/ohm/libohm_cgroups.so /usr/lib/ohm/libohm_cgroups.so.disabled
2. reboot your phone
ohmd will start but without cgroup module, /syspart/ will not be mounted and desktop reactions are faster and every process have same cpu-share. just like in normal linux desktop like in ubuntu/debian/...
3. enjoy

On my device this causes live wallpaper to fail to load at boot. undoing this modification returns live wallpaper to it's normal behavior.