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

On Fri, 2012-07-06 at 15:30 -0500, Christoph Lameter wrote:

On Fri, 6 Jul 2012, James Bottomley wrote:

quoted

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.