Re: [ofa-general] Re: [ewg] Re: [PATCH] IB/ehca: Serialize HCA-related hCalls on POWER5

caitlin.bestler@gmail.com wrote on 13.12.2007 20:22:49:

On Dec 13, 2007 12:30 AM, Or Gerlitz [off-list ref] wrote:

quoted

The current implementation of the open iscsi initiator makes sure to
issue commands in thread (sleepable) context, see iscsi_xmitworker and
references to it in drivers/scsi/libiscsi.c , so this keeps ehca users
safe for the time being.

I agree, *some* form of FMR support is important for iSER (and probably
for NFS over RDMA as well). Rather than adding a crippled NO FMR
mode it would make more sense to add support for FMR Work Requests.
I'm not certain what, if any, impact that would have on the Power5 

problem,

but that's certainly a cleaner path for iWARP.

Well, FMR WRs wouldn't change the eHCA issue -- the driver would have to 
make an hCall in any case, and the architecture says that the hCalls used 
in this scenario might return H_LONG_BUSY, causing the driver to sleep. No 
way around that. Because of this, eHCA's FMRs are actually standard MRs 
with a different API.

If, as Or said, the iSCSI initiator issues commands in sleepable context 
anyway, nothing would be lost by using standard MRs as a fallback solution 
if FMRs aren't available, would it?

J.