RE: [PATCH] SCSI driver for VMware's virtual HBA.

[Alok Kataria <akataria@vmware.com>]

Hi Chetan,

On Fri, 2009-08-28 at 14:18 -0700, Chetan.Loke@Emulex.Com wrote:
> Alok,
> 
> 
> > +static int __devinit pvscsi_allocate_rings(struct pvscsi_adapter
> > *adapter)
> > +{
> > +	adapter->rings_state = pci_alloc_consistent(adapter->dev, PAGE_SIZE,
> > +						    &adapter->ringStatePA);
> > +	if (!adapter->rings_state)
> > +		return -ENOMEM;
> > +
> > +	adapter->req_pages = min(PVSCSI_MAX_NUM_PAGES_REQ_RING,
> > +				 pvscsi_ring_pages);
> > +	adapter->req_depth = adapter->req_pages
> > +					* PVSCSI_MAX_NUM_REQ_ENTRIES_PER_PAGE;
> > +	adapter->req_ring = pci_alloc_consistent(adapter->dev,
> > +						 adapter->req_pages * PAGE_SIZE,
> > +						 &adapter->reqRingPA);
> > +	if (!adapter->req_ring)
> > +		return -ENOMEM;
> > +
> > +	adapter->cmp_pages = min(PVSCSI_MAX_NUM_PAGES_CMP_RING,
> > +				 pvscsi_ring_pages);
> > +	adapter->cmp_ring = pci_alloc_consistent(adapter->dev,
> > +						 adapter->cmp_pages * PAGE_SIZE,
> > +						 &adapter->cmpRingPA);
> > +	if (!adapter->cmp_ring)
> > +		return -ENOMEM;
> > +
> > +	BUG_ON(adapter->ringStatePA & ~PAGE_MASK);
> > +	BUG_ON(adapter->reqRingPA   & ~PAGE_MASK);
> > +	BUG_ON(adapter->cmpRingPA   & ~PAGE_MASK);
> > +
> > +	if (!adapter->use_msg)
> > +		return 0;
> > +
> > +	adapter->msg_pages = min(PVSCSI_MAX_NUM_PAGES_MSG_RING,
> > +				 pvscsi_msg_ring_pages);
> > +	adapter->msg_ring = pci_alloc_consistent(adapter->dev,
> > +						 adapter->msg_pages * PAGE_SIZE,
> > +						 &adapter->msgRingPA);
> > +	if (!adapter->msg_ring)
> > +		return -ENOMEM;
> > +	BUG_ON(adapter->msgRingPA & ~PAGE_MASK);
> > +
> > +	return 0;
> > +}
> > +
> 
> I understand the emulation etc. But I see that this function isn't
> allocating multiple rings right? Didn't see any performance benefits?
> 

The function is allocating multiple rings, actually 2 of them for the
IO path, request and completion rings (req_ring, cmp_ring). 

Let me know if you were asking something else.

Thanks,
Alok

> 
> 
> Chetan
> 
> 
> 
>