IO impacting systems responsiveness

[Ryan Bair]

Which I/O scheduler are you using? I've had a lot of issues with CFQ
starving low i/o processes when the system was under even moderate
load. I switched to deadline and it's 1000x better. I'm on Debian
Etch.

The nice thing about deadline is that it tries to get things done in a
reasonable timeframe. Raw speed is usually a tiny bit lower that other
schedulers, but is so much more responsive under load its not funny.
I've often wondered how CFQ became the default...

On Nov 17, 2007 9:53 AM, Peter Grandi <pg_dlxpe at dlxpe.for.sabi.co.uk> wrote:
> >>> On Thu, 15 Nov 2007 11:57:00 -0800 (PST), Antonio Varni
> >>> <avarni at estalea.com> said:
>
> avarni> Hello everyone.  I'm wondering what other people's
> avarni> experiences are WRT systems becoming unresponsive
> avarni> (unable to ssh in, etc) for brief periods of time when a
> avarni> large amount of IO is being performed.
>
> It is extremely common. It is particularly irritating during
> desktop use, where periods of intense IO (e.g. system updates,
> ...) often result in the apparent freezing of the GUI.
>
> avarni> All mysql data files are on a netapp filer but mysql's
> avarni> tmp directory is on local disk.  Whenever a lot of temp
> avarni> tables are created (and this written and deleted from
> avarni> local disk quickly) we can't even log in to the machine
>
> That's how it should work with the default parameters for the IO
> subsystem (caching, elevators, ...). These are perhaps not
> wisely chosen, and tend to favour throughput over latency.
>
> avarni> Is it just me? Or is this specific to Dell systems, or
> avarni> is this just the state of the Linux kernel these days?
>
> It is the state of the default configuration of the Linux kernel
> IO subsystem coupled with buffering behaviour of host adapters.
> Very different results can be chosen by changing the defaults.
>
>
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