Re: linux deadline i/o elevator tuning

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От Kevin Grittner
Тема Re: linux deadline i/o elevator tuning
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Msg-id 49DDC697.EE98.0025.0@wicourts.gov
обсуждение исходный текст
Ответ на Re: linux deadline i/o elevator tuning  (Arjen van der Meijden)
Список pgsql-performance
Дерево обсуждения
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, )
Arjen van der Meijden <> wrote:
> On 9-4-2009 16:09 Kevin Grittner wrote:
>> I haven't benchmarked it, but when one of our new machines seemed a
>> little sluggish, I found this hadn't been set.  Setting this and
>> rebooting Linux got us back to our normal level of performance.
>
> Why would you reboot after changing the elevator? For 2.6-kernels,
> it can be adjusted on-the-fly for each device separately
> (echo 'deadline' > /sys/block/sda/queue/scheduler).

On the OS where this happened, not yet an option:

kgrittn@DBUTL-PG:~> cat /proc/version
Linux version 2.6.5-7.315-bigsmp (geeko@buildhost) (gcc version 3.3.3
(SuSE Linux)) #1 SMP Wed Nov 26 13:03:18 UTC 2008
kgrittn@DBUTL-PG:~> ls -l /sys/block/sda/queue/
total 0
drwxr-xr-x  2 root root    0 2009-03-06 15:27 iosched
-rw-r--r--  1 root root 4096 2009-03-06 15:27 nr_requests
-rw-r--r--  1 root root 4096 2009-03-06 15:27 read_ahead_kb

On machines built more recently than the above, I do see a scheduler
entry in the /sys/block/sda/queue/ directory.  I didn't know about
this enhancement, but I'll keep it in mind.  Thanks for the tip!

> Apart from deadline, 'noop' should also be interesting for RAID and
> SSD-owners, as it basically just forwards the I/O-request to the
> device and doesn't do much (if any?) scheduling.

Yeah, I've been tempted to give that a try, given that we have BBU
cache with write-back.  Without a performance problem using elevator,
though, it hasn't seemed worth the time.

-Kevin

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