Re: linux deadline i/o elevator tuning

От: Kevin Grittner
Тема: Re: linux deadline i/o elevator tuning
Дата: ,
Msg-id: 49E31168.EE98.0025.0@wicourts.gov
(см: обсуждение, исходный текст)
Ответ на: Re: linux deadline i/o elevator tuning  (Jeff)
Список: pgsql-performance

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linux deadline i/o elevator tuning  (Mark Wong, )
 Re: linux deadline i/o elevator tuning  ("Kevin Grittner", )
  Re: linux deadline i/o elevator tuning  (Grzegorz Jaśkiewicz, )
   Re: linux deadline i/o elevator tuning  (Matthew Wakeling, )
    Re: linux deadline i/o elevator tuning  (Grzegorz Jaśkiewicz, )
     Re: linux deadline i/o elevator tuning  ("Kevin Grittner", )
      Re: linux deadline i/o elevator tuning  (Grzegorz Jaśkiewicz, )
     Re: linux deadline i/o elevator tuning  (Matthew Wakeling, )
    Re: linux deadline i/o elevator tuning  ("Kevin Grittner", )
   Re: linux deadline i/o elevator tuning  (Scott Carey, )
   Re: linux deadline i/o elevator tuning  ("Albe Laurenz *EXTERN*", )
    Re: linux deadline i/o elevator tuning  (Jeff, )
     Re: linux deadline i/o elevator tuning  ("Kevin Grittner", )
  Re: linux deadline i/o elevator tuning  (Arjen van der Meijden, )
   Re: linux deadline i/o elevator tuning  ("Kevin Grittner", )
 Re: linux deadline i/o elevator tuning  (Mark Wong, )
  Re: linux deadline i/o elevator tuning  (Mark Wong, )

Jeff <> wrote:

> If you have a halfway OK raid controller, CFQ is useless. You can
fire
> up something such as pgbench or pgiosim, fire up an iostat and then

> watch your iops jump high when you flip to noop or deadline and
> plummet on cfq.

An interesting data point, but not, by itself, conclusive.  One of the
nice things about a good scheduler is that it allows multiple writes
to the OS to be combined into a single write to the controller cache.
I think that having a large OS cache and the deadline elevator allowed
us to use what some considered extremely aggressive background writer
settings without *any* discernible increase in OS output to the disk.
The significant measure is throughput from the application point of
view; if you see that drop as cfq causes the disk I/O to drop, *then*
you've proven your point.

Of course, I'm betting that's what you do see....

-Kevin


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