Karmic I/O scheduler issues

Tim Gardner tim.gardner at canonical.com
Tue Sep 29 20:37:24 UTC 2009

I've been messing with I/O scheduler settings in the last couple of
uploads. We found that CFQ has some serious issues that contributed to
delayed boot times, so I changed the default to Deadline in
2.6.31-10.35. Scott Remnant reported that changing to Deadline shaved 40
seconds off his boot.

Since then I found this info: http://bugs.launchpad.net/bugs/436342

I've been running a kernel with this patch and CFQ enabled. Perhaps some
other folks could compare and contrast Deadline v.s. CFQ using their
workloads. I find that CFQ is working a bit better then Deadline. I can
run a 'make -j8' kernel build and still watch video while also playing
music and reading email (without _too_ much stalling). Deadline is
noticeably less smooth when the load average approaches 8.

Adventurous types can try this kernel from

(when its done copying)

You can swizzle your I/O scheduler settings thusly:

cat /sys/block/$YOUR_BLOCK_DEVICE/queue/schedule
echo cfq | sudo tee /sys/block/$YOUR_BLOCK_DEVICE/queue/scheduler

Tim Gardner tim.gardner at canonical.com

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