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

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Message-Id: <1251755593.16169.51.camel@ank32.eng.vmware.com>
Date:	Mon, 31 Aug 2009 14:53:13 -0700
From:	Alok Kataria <akataria@...are.com>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Robert Love <robert.w.love@...el.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Mike Christie <michaelc@...wisc.edu>,
	"linux-scsi@...r.kernel.org" <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>,
	Bhavesh Davda <bhavesh@...are.com>
Subject: Re: [PATCH] SCSI driver for VMware's virtual HBA.

Hi James, 

Thanks for your comments. 

On Mon, 2009-08-31 at 11:00 -0700, James Bottomley wrote:
> On Mon, 2009-08-31 at 10:28 -0700, Alok Kataria wrote:
> > VMware PVSCSI driver - v2.
> 
> OK, so the first thing that springs to mind is that we already have one
> of these things: the ibmvscsi ... is there no way we can share code
> between this and the other PV drivers?

I took a quick look at the ibmvscsi driver, and there are lot of
differences between the two, mainly the ABI that is shared between the
hypervisor and driver differ. Also the ibmvscsi driver seems to offer a
lot of other features as well, like the SRP. 

The pvscsi driver is a simple SCSI adapter driver and is basically no
different than any other SCSI driver written for a particular HBA.

> 
> > Changelog (v2-v1)
> > - use PCI_VDEVICE instead of PCI_DEVICE.
> > - use list_first_entry
> > - use parenthesis for every sizeof usage
> > - get rid of all #ifdef for CONFIG_PCI_MSI
> > - use PVSCSI_MEM_SPACE_SIZE while checking for MMIO resource len.
> > - use kcalloc instead of kmalloc.
> > - replaced a couple of scmd_printk usage with dev_dbg
> > - use dev_info and pr_info at couple of places.
> > - add a comment to pvscsi_map_context
> > - Add entry in MAINTAINERS.
> > 
> > Patch applies on top of 2.6.31-rc8.
> > --
> > 
> > SCSI driver for VMware's virtual HBA.
> > 
> > From: Alok N Kataria <akataria@...are.com>
> > 
> > This is a driver for VMware's paravirtualized SCSI device,
> > which should improve disk performance for guests running
> > under control of VMware hypervisors that support such devices.
> > 
> > Signed-off-by: Alok N Kataria <akataria@...are.com>
> > ---
> > 
> >  MAINTAINERS           |    7 
> >  drivers/scsi/Kconfig  |    8 
> >  drivers/scsi/Makefile |    1 
> >  drivers/scsi/pvscsi.c | 1391 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  drivers/scsi/pvscsi.h |  395 ++++++++++++++
> >  5 files changed, 1802 insertions(+), 0 deletions(-)
> >  create mode 100644 drivers/scsi/pvscsi.c
> >  create mode 100644 drivers/scsi/pvscsi.h
> > 
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 60299a9..952fe93 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -5491,6 +5491,13 @@ S:	Maintained
> >  F:	drivers/vlynq/vlynq.c
> >  F:	include/linux/vlynq.h
> >  
> > +VMware PVSCSI driver
> > +M:	Alok Kataria <akataria@...are.com>
> > +L:	linux-scsi@...r.kernel.org
> > +S:	Maintained
> > +F:	drivers/scsi/pvscsi.c
> > +F:	drivers/scsi/pvscsi.h
> > +
> >  VOLTAGE AND CURRENT REGULATOR FRAMEWORK
> >  M:	Liam Girdwood <lrg@...mlogic.co.uk>
> >  M:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
> > diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
> > index 9c23122..8a47981 100644
> > --- a/drivers/scsi/Kconfig
> > +++ b/drivers/scsi/Kconfig
> > @@ -620,6 +620,14 @@ config SCSI_FLASHPOINT
> >  	  substantial, so users of MultiMaster Host Adapters may not
> >  	  wish to include it.
> >  
> > +config VMWARE_PVSCSI
> > +	tristate "VMware PVSCSI driver support"
> > +	depends on PCI && SCSI && X86
> 
> This is a PCI emulation driver ... it shouldn't be x86 only.

VMware virtualizes only x86 hardware, as a result this device will be
available for use only on x86 systems, so I don't think allowing it for
other arch's matters as such. Apart from that, the driver relies on some
memory ordering semantics which the X86 follows. This is done to
optimize the driver code and avoid using expensive memory barriers which
are not needed on x86. I have added comments in the driver code for
these cases.

> 
> > +	help
> > +	  This driver supports VMware's para virtualized SCSI HBA.
> > +	  To compile this driver as a module, choose M here: the
> > +	  module will be called pvscsi.
> > +
> >  config LIBFC
> >  	tristate "LibFC module"
> >  	select SCSI_FC_ATTRS
> > diff --git a/drivers/scsi/Makefile b/drivers/scsi/Makefile
> > index 25429ea..27fd013 100644
> > --- a/drivers/scsi/Makefile
> > +++ b/drivers/scsi/Makefile
> > @@ -130,6 +130,7 @@ obj-$(CONFIG_SCSI_MVSAS)	+= mvsas/
> >  obj-$(CONFIG_PS3_ROM)		+= ps3rom.o
> >  obj-$(CONFIG_SCSI_CXGB3_ISCSI)	+= libiscsi.o libiscsi_tcp.o cxgb3i/
> >  obj-$(CONFIG_SCSI_BNX2_ISCSI)	+= libiscsi.o bnx2i/
> > +obj-$(CONFIG_VMWARE_PVSCSI)	+= pvscsi.o
> >  
> >  obj-$(CONFIG_ARM)		+= arm/
> >  
> > diff --git a/drivers/scsi/pvscsi.c b/drivers/scsi/pvscsi.c
> > new file mode 100644
> > index 0000000..fc85a3a
> > --- /dev/null
> > +++ b/drivers/scsi/pvscsi.c
> [...]
> > +static int __devinit pvscsi_allocate_sg(struct pvscsi_adapter *adapter)
> > +{
> > +	struct pvscsi_ctx *ctx;
> > +	int i;
> > +
> > +	ctx = adapter->cmd_map;
> > +	BUILD_BUG_ON(sizeof(struct pvscsi_sg_list) > PAGE_SIZE);
> > +
> > +	for (i = 0; i < adapter->req_depth; ++i, ++ctx) {
> > +		ctx->sgl = pci_alloc_consistent(adapter->dev, PAGE_SIZE,
> > +						&ctx->sglPA);
> 
> Why do you need coherent memory for the sg list?  Surely the use pattern
> of an SG list is that it follows a predefined ownership model between
> the driver and the virtual device, thus not really requiring coherent
> memory?

The SG list needs to be accessed by the hypervisor too, and we need the
physical address to access it from the hypervisor. We do that using the
sglPA field right now, which the pci_.. interface returns.  Do you think
something else should be used for that purpose ? 

Alok

> > +		BUG_ON(ctx->sglPA & ~PAGE_MASK);
> > +		if (!ctx->sgl) {
> > +			for (; i >= 0; --i, --ctx) {
> > +				pci_free_consistent(adapter->dev, PAGE_SIZE,
> > +						    ctx->sgl, ctx->sglPA);
> > +				ctx->sgl = NULL;
> > +				ctx->sglPA = 0;
> > +			}
> > +			return -ENOMEM;
> > +		}
> > +	}
> > +
> > +	return 0;
> > +}
> 
> James
> 
> 

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