Karmic I/O scheduler issues

Tim Gardner tim.gardner at canonical.com
Tue Sep 29 23:31:27 UTC 2009

Tim Gardner wrote:
> 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
> http://kernel.ubuntu.com/~rtg/2.6.31-11-NEW_FAIR_SLEEPERS
> (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
> rtg

There is some good discussion about I/O scheduling and SSDs from Colin King:


Tim Gardner tim.gardner at canonical.com

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