Re: [Ksummit-2012-discuss] SCSI Performance regression [was Re: [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6]

["Nicholas A. Bellinger" <nab@xxxxxxxxxxxxxxx>]

On Fri, 2012-07-06 at 15:30 -0500, Christoph Lameter wrote:
> On Fri, 6 Jul 2012, James Bottomley wrote:
> 
> > What people might pay attention to is evidence that there's a problem in
> > 3.5-rc6 (without any OFED crap).  If you're not going to bother
> > investigating, it has to be in an environment they can reproduce (so
> > ordinary hardware, not infiniband) otherwise it gets ignored as an
> > esoteric hardware issue.
> 
> The OFED stuff in the meantime is part of 3.5-rc6. Infiniband has been
> supported for a long time and its a very important technology given the
> problematic nature of ethernet at high network speeds.
> 
> OFED crap exists for those running RHEL5/6. The new enterprise distros are
> based on the 3.2 kernel which has pretty good Infiniband support
> out of the box.
> 

So I don't think the HCAs or Infiniband fabric was the limiting factor
for small block random I/O in the RHEL 6.2 w/ OFED vs. Windows Server
2008 R2 w/ OFED setup mentioned earlier.

I've seen both FC and iSCSI fabrics demonstrate the same type of random
small block I/O performance anomalies with Linux/SCSI clients too.  The
v3.x Linux/SCSI clients are certainly better in the multi-lun per host
small block random I/O case, but single LUN performance is (still)
lacking compared to everything else.

Also RHEL 6.2 does have the scsi-host-lock less bits in place now, but
it's been more a matter of converting OFED ib_srp code to run in
host-lock less mode to realize extra gains for multi-lun per host.

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