Arjen van der Meijden <acmmailing(at)tweakers(dot)net> 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(at)DBUTL-PG:~> cat /proc/version
Linux version 2.6.5-7.315-bigsmp (geeko(at)buildhost) (gcc version 3.3.3
(SuSE Linux)) #1 SMP Wed Nov 26 13:03:18 UTC 2008
kgrittn(at)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