linux-kernel - Re: [PATCH] SCSI driver for VMware's virtual HBA.

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Message-ID: <e2e108260909010934k7be05930lfa544ea914224cf1@mail.gmail.com>
Date:	Tue, 1 Sep 2009 18:34:30 +0200
From:	Bart Van Assche <bvanassche@....org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	James Bottomley <James.Bottomley@...e.de>, akataria@...are.com,
	Robert Love <robert.w.love@...el.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Mike Christie <michaelc@...wisc.edu>,
	linux-scsi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Torokhov <dtor@...are.com>,
	Rolf Eike Beer <eike-kernel@...tec.de>,
	Maxime Austruy <maustruy@...are.com>
Subject: Re: [PATCH] SCSI driver for VMware's virtual HBA.

On Tue, Sep 1, 2009 at 6:12 PM, Roland Dreier <rdreier@...co.com> wrote:
>  > - Reuse the ib_ipoib kernel module to provide an IP stack on top of
>  > the new RDMA driver instead of having to maintain a separate network
>  > driver for this hardware (ibmveth).
>
> I don't think this really makes sense, because IPoIB is not really
> handling ethernet (it is a different L2 ethernet encapsulation), and I
> think the commonality with ibmveth is going to be minimal.

What I had in mind was not to start searching for code shared between
the ipoib and ibmveth kernel modules, but to replace the virtual
Ethernet layer by IPoIB on top of a new RDMA driver. I'm not sure
however this approach would work better than the currently implemented
approach in ibmveth.

> I'm not really sure we should be trying to force drivers to share just
> because they are paravirtualized -- if there is real commonality, then
> sure put it in common code, but different hypervisors are probably as
> different as different hardware.

Agreed. But several people are currently looking at how to improve the
performance of I/O performed inside a virtual machine without being
familiar with the VIA architecture or the RDMA API. This is a pity
because the Virtual Interface Architecture was designed to allow
high-throughput low-latency I/O, and has some features that are not
present in any other mainstream I/O architecture I know of (e.g. the
ability to perform I/O from userspace without having to invoke any
system call in the performance-critical path).

Bart.
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