[Lustre-discuss] high CPU load limits bandwidth?

Michael Kluge Michael.Kluge at tu-dresden.de
Wed Oct 20 07:41:17 PDT 2010


Hi list,

is it normal, that a 'dd' or an 'IOR' pushing 10MB blocks to a lustre
file system shows up with a 100% CPU load within 'top'? The reason why I
am asking this is that I can write from one client to one OST with 500
MB/s. The CPU load will be at 100% in this case. If I stripe over two
OSTs (which use different OSS servers and different RAID controllers) I
will get 500 as well (seeing 2x250 MB/s on the OSTs). The CPU load will
be at 100% again. 

A 'dd' on my desktop pushing 10M blocks to the local disk shows 7-10%
CPU load.

Are there ways to tune this behavior? Changing max_rpcs_in_flight and
max_dirty_mb did not help.


Regards, Michael

-- 

Michael Kluge, M.Sc.

Technische Universität Dresden
Center for Information Services and
High Performance Computing (ZIH)
D-01062 Dresden
Germany

Contact:
Willersbau, Room A 208
Phone:  (+49) 351 463-34217
Fax:    (+49) 351 463-37773
e-mail: michael.kluge at tu-dresden.de
WWW:    http://www.tu-dresden.de/zih
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