[Lustre-discuss] lustre client /proc cached reads

[Andreas Dilger]

On Aug 01, 2008  14:29 -0400, John Parhizgari wrote:
> After doing a few experimental read tests while examining 
> /proc/fs/lustre/osc/OSTID/stats on the lustre client:
> 
> It seems to be that the 7th column of the stats file, on the ost_read 
> line, represents the total bytes read for all the RPC calls involving 
> reading from that OST up until now (2773483520 in the example below).
> ost_read                  91655 samples [usec] 4096 1048576 2773483520 
> 1759238200229888
> 
> Is this an accurate description of ost_read?

Yes, though unfortunately this statistic was "hijacked" from being
the per-RPC latency (hence [usec] units).  I've attached a patch to
bug 16573 that fixes this, though it is still just a prototype.

> If so, does it make sense to use information to track and analyze the 
> true read stats against OSTs and filesystems (since the llite stats 
> includes client-cached data reads)? And then also similarly for 
> ost_write, since we want essentially Lustre's network activity to the 
> filesystem; if the above holds this will be representative of how much 
> data is really being transferred to/from the lustre filesystems for each 
> client.

The above patch also tracks these stats on the OST.  See also "brw_stats"
and "rpc_stats" on the obdfilter devices.

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