[Lustre-discuss] high CPU load limits bandwidth?

Michael Kluge Michael.Kluge at tu-dresden.de
Wed Oct 20 09:40:10 PDT 2010


It is the CPU load on the client. The dd/IOR process is using one core 
completely. The clients and the servers are connected via DDR IB. LNET 
bandwidth is at 1.8 GB/s. Servers have 1.8.3, the client has 1.8.3 
patchless.


Micha

Am 20.10.2010 18:15, schrieb Andreas Dilger:
> Is this client CPU or server CPU?  If you are using Ethernet it will definitely be CPU hungry and can easily saturate a single core.
>
> Cheers, Andreas
>
> On 2010-10-20, at 8:41, Michael Kluge<Michael.Kluge at tu-dresden.de>  wrote:
>
>> 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
>> _______________________________________________
>> Lustre-discuss mailing list
>> Lustre-discuss at lists.lustre.org
>> http://lists.lustre.org/mailman/listinfo/lustre-discuss
>


-- 
Michael Kluge, M.Sc.

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

Contact:
Willersbau, Room WIL 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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