Re: Linux I/O tuning: CFQ vs. deadline

On Tue, Feb 9, 2010 at 11:37 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> Jeff wrote:
>>
>> I'd done some testing a while ago on the schedulers and at the time
>> deadline or noop smashed cfq.  Now, it is 100% possible since then that
>> they've made vast improvements to cfq and or the VM to get better or similar
>> performance.  I recall a vintage of 2.6 where they severely messed up the
>> VM. Glad I didn't upgrade to that one :)
>>
>> Here's the old post:
>> http://archives.postgresql.org/pgsql-performance/2008-04/msg00155.php
>
> pgiosim doesn't really mix writes into there though, does it?  The mixed
> read/write situations are the ones where the scheduler stuff gets messy.

I agree. I think the only way to really test it is by testing it
against the system it's got to run under. I'd love to see someone do
a comparison of early to mid 2.6 kernels (2.6.18 like RHEL5) to very
up to date 2.6 kernels. On fast hardware. What it does on a laptop
isn't that interesting and I don't have a big machine idle to test it
on.