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SubjectRe: Where is the performance bottleneck?
* Holger Kiehl (Holger.Kiehl@dwd.de) wrote:

> There is however one difference, here I had set
> /sys/block/sd?/queue/nr_requests to 4096.

Well from that it looks like none of the queues get about 255
(hmm that's a round number....)

> avg-cpu: %user %nice %sys %iowait %idle
> 0.10 0.00 21.85 58.55 19.50

Fair amount of system time.

> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s
> avgrq-sz avgqu-sz await svctm %util

> sdf 11314.90 0.00 365.10 0.00 93440.00 0.00 46720.00 0.00
> 255.93 1.92 5.26 2.74 99.98
> sdg 7973.20 0.00 257.20 0.00 65843.20 0.00 32921.60 0.00
> 256.00 1.94 7.53 3.89 100.01

There seems to be quite a spread of read performance accross the drives
(pretty consistent accross the run); what makes sdg so much slower than
sdf (which seems to be the slowest and fastest drives respectively).
I guess if everyone was running at sdf's speed you would be pretty happy.

If you physically swap f and g does the performance follow the drive
or the letter?

Dave
--
-----Open up your eyes, open up your mind, open up your code -------
/ Dr. David Alan Gilbert | Running GNU/Linux on Alpha,68K| Happy \
\ gro.gilbert @ treblig.org | MIPS,x86,ARM,SPARC,PPC & HPPA | In Hex /
\ _________________________|_____ http://www.treblig.org |_______/
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