[Lustre-discuss] Slow warnings

Andreas Dilger adilger at sun.com
Fri Aug 28 12:46:48 PDT 2009


On Aug 28, 2009  15:00 -0400, Scott Atchley wrote:
> I am testing with MXLND. My setup is very simple. I have one MGS/MDT,  
> one OST, and one client. All are running RHEL5.3. The OST is using a  
> loopback device on the internal disk which is capable of ~70 MB/s.

Note that using a loopback device imposes a lot of extra overhead on
the OST.  There is an extra data copy inside the driver, and there
are 2 levels of "transactions", one for the loopback ldiskfs filesystem,
and one for the underlying (assumed ext3) filesystem.

> I am running 10 dd in parallel which send 1 GB each and MXLND should  
> be able to send the data ~1,100 MB/s. The machine has 8 GB of memory.  

> Before the dds complete, free memory drops to about 32 MB. Everything  
> completes, but Lustre posts the following to dmesg:
> 
> Lustre: 4227:0:(filter_io_26.c:641:filter_commitrw_write()) lustre- 
> OST0000: slow i_mutex 30s
> Lustre: 4222:0:(lustre_fsfilt.h:320:fsfilt_commit_wait()) lustre- 
> OST0000: slow journal start 30s
> Lustre: 4222:0:(filter_io_26.c:724:filter_commitrw_write()) lustre- 
> OST0000: slow commitrw commit 30s
> Lustre: 4242:0:(filter_io_26.c:706:filter_commitrw_write()) lustre- 
> OST0000: slow direct_io 30s
> Lustre: 4242:0:(filter_io_26.c:706:filter_commitrw_write()) Skipped 4  
> previous similar messages
> 
> Should I be concerned or is this normal?

If you are just testing the MXLND you could also use LNET Self Test
(LST) and avoid the OST entirely.  Alternately, to do Lustre RPC level
testing you can use echo server.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.




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