[ofw] choice between IBAL and winverbs

[Smith, Stan]

________________________________
From: Sivaselvam Narayanasamy [mailto:sivaselvam.narayanasamy at oracle.com]
Sent: Tuesday, July 21, 2009 11:36 AM
To: Smith, Stan
Cc: Prasanna Vv; ofw at lists.openfabrics.org; Sivaselvam Narayanasamy
Subject: RE: [ofw] choice between IBAL and winverbs

Stan,

Prasanna's question may be :  From a kernel mode driver,  which is the preferred route, to talk to the layers below :-

a) through the winverbs.sys driver ( available in WinOF 2.1 )  or
b) through the IBAL kernel driver

?

I'm not a Windows driver or winverbs expert, Sean and Fab are the guys who wrote the code - guys please chime in.

Kernel mode IB verbs clients in the WinOF stack use a direct call interface. The IPoIB driver requests an IBAL kernel interface based on a well-known GUID. IBAL returns an interface struct populated at runtime with IBAL function pointers from the ibal verbs driver (aka ibbus.sys) memory image.

The ibbus.sys driver (an upper class filter driver for an InfiniBand Controller (aka HCA)) creates a DOS file/ IOCTL() interface so user-mode apps can access IBAL verbs functionality.
The difference between user-mode IBAL and kernel mode IBAL is IOCTL() vs. direct-call interfaces.
Other considerations:
   Marshalling of arguments
   accessibility of args
      inputs -[direct access or copyin()].
      outputs -  [direct access or copyout()].

Winverbs does not export a kernel mode direct-call interface at this time; winverbs only exports an IOCTL() interface accessible only from user mode.

The  only kernel mode verbs interface choice at this time is to use IBAL.

Hopefully this clears up any confusion.

stan.

Thanks
Siva
-----Original Message-----
From: ofw-bounces at lists.openfabrics.org [mailto:ofw-bounces at lists.openfabrics.org]On Behalf Of Smith, Stan
Sent: Tuesday, July 21, 2009 10:52 PM
To: Prasanna Vv; ofw at lists.openfabrics.org
Subject: RE: [ofw] choice between IBAL and winverbs

________________________________
From: ofw-bounces at lists.openfabrics.org [mailto:ofw-bounces at lists.openfabrics.org] On Behalf Of Prasanna Vv
Sent: Tuesday, July 21, 2009 10:16 AM
To: ofw at lists.openfabrics.org
Subject: Re: [ofw] choice between IBAL and winverbs

Thanks Stan.
For kernel mode IB  interface,  whether  winverbs-driver IOCTL can be used or IBAL is the only choice?

Unfortunately I was not clear w.r.t. user-mode or kernel mode POV (Point-Of-View).
A kernel mode implementation of winverbs is not available today. The work is being discussed and will be available in the WinOF 2.2 release (late Q4'09/Q1'10).
Kernel mode winverbs will not be available in the upcoming WinOF 2.1 release.

stan.

Regards,
Prasanna

Smith, Stan wrote:

Prasanna Vv wrote:


Hello All,

In WINOF 2.1, most of the ULPs are based on Winverbs, while IPoIB
driver continues to use IBAL .



Actually most of the ULPs are based on IBAL for historical reasons.
It's only newer DAPL providers (Socket-CM & rdma-CM) plus OFED diags which are using OFED compatibility (aka libibverbs/winverbs).
NetworkDirect continues to use the IBAL IF although there is work-in-progress to switch over to winverbs to take advantage of overlapped I/O ops.



I wish to know if OFED will continue to support and enhance IBAL as
complimentary approach for Winverbs for IB verbs interface ?  Or IBAL
may be phased out ?



The IBAL interface will be supported well into the future, measured in years.
Under the covers, how the IBAL interface is implemented may change such that an IBAL function could transparently become a wrapper for a call into winverbs.
The 'BIG" deal with IBAL is how it implements PNP and how IPoIB and drivers rely on this implementation.
There are no current plans to change all drivers and IPoIB to use Microsoft PNP and remove this functionality from IBAL; although it would be an excellent idea (very large task). For the PNP reasons, IBAL will stick around for some time.

For future development, I would recommend the OFED compatibility layer (libibverbs/winverbs).

Stan.



Thanks,
Prasanna

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