Wrong SD card IO scheduler


4 posts
by Zielony » Sun Jan 13, 2013 10:24 am
As Raspberry runs by default on SD card, there should be special care of IO scheduler of that device. Unfortunately I noticed today the scheduler is set to CFQ looking into /sys/block/mmcblk0/queue/scheduler. To change it do deadline I created /etc/tmpfiles.d/set_IO_scheduler.conf with such content:
Code: Select all
w /sys/block/mmcblk0/queue/scheduler - - - - deadline

I hope SD IO performance will be much better now. But in my opinion this setting should be guaranteed since pure installation.
Posts: 9
Joined: Thu Jan 03, 2013 4:20 pm
by pepedog » Sun Jan 13, 2013 11:06 am
I am no expert in this matter and inclined to blindly follow this
Next rootfs had/has elevator=noop in cmdline.txt so I get
cat /sys/block/mmcblk0/queue/scheduler
[noop] deadline cfq
So elevator=deadline would do it?
Hmm, noop seemed faster in my slow card

My fast card
Code: Select all
echo "deadline" > /sys/block/mmcblk0/queue/scheduler
# dd if=/dev/zero of=test bs=1M count=512
536870912 bytes (537 MB) copied, 34.6949 s, 15.5 MB/s
# echo "noop" > /sys/block/mmcblk0/queue/scheduler
# dd if=/dev/zero of=test bs=1M count=512
536870912 bytes (537 MB) copied, 35.3581 s, 15.2 MB/s

My slow card was .3 quicker too with noop
I'm still no expert on this
Posts: 960
Joined: Fri Oct 07, 2011 9:55 am
by Zielony » Sun Jan 13, 2013 11:43 am
Neither I'm not an expert. I hadn't tested it before. Also with my class 10 card seems to be a bit faster with noop.

Code: Select all
root:~# echo "deadline" > /sys/block/mmcblk0/queue/scheduler
root:~# sync
root:~# dd if=/dev/zero of=test bs=1M count=128
128+0 records in
128+0 records out
134217728 bytes (134 MB) copied, 14.0027 s, 9.6 MB/s
root:~# sync
root:~# echo "noop" > /sys/block/mmcblk0/queue/scheduler
root:~# sync
root:~# dd if=/dev/zero of=test bs=1M count=128
128+0 records in
128+0 records out
134217728 bytes (134 MB) copied, 13.1649 s, 10.2 MB/s


If /sys/block/mmcblk0/queue/scheduler shows noop, elevator seems to work. ;)

BTW it's very nice to see that someone cares about making distro better and better.
Posts: 9
Joined: Thu Jan 03, 2013 4:20 pm
by pepedog » Sun Jan 13, 2013 2:22 pm
Nice to see others giving input too, even though I'm just fumbling my way around arch is very underrated. Mandriva and I think fedora has systemd, plus geexbox and possibly mer.
We have considered making larger images that would be for games/karaoke/media/dev. Foundation can't host these though.
Posts: 960
Joined: Fri Oct 07, 2011 9:55 am