[Lustre-discuss] high CPU load limits bandwidth?

Bernd Schubert bs_lists at aakef.fastmail.fm
Wed Oct 20 09:33:07 PDT 2010


That is normal and probably comes from the page cache, should be about the 
same for lustre, ldiskfs, ext4, xfs, etc. It goes down if you specify 
"-odirect", but which is obviously not optimal on Lustre clients.


Cheers,
Bernd

On Wednesday, October 20, 2010, Andreas Dilger wrote:
> 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
> 
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