svn commit: r209026 - in head/sys/ia64: ia64 include

[Scott Long]

On Jun 11, 2010, at 5:51 AM, John Baldwin wrote:
> On Thursday 10 June 2010 11:00:33 pm Marcel Moolenaar wrote:
>> Author: marcel
>> Date: Fri Jun 11 03:00:32 2010
>> New Revision: 209026
>> URL: http://svn.freebsd.org/changeset/base/209026
>> 
>> Log:
>> Bump MAX_BPAGES from 256 to 1024. It seems that a few drivers, bge(4)
>> in particular, do not handle deferred DMA map load operations at all.
>> Any error, and especially EINPROGRESS, is treated as a hard error and
>> typically abort the current operation. The fact that the busdma code
>> queues the load operation for when resources (i.e. bounce buffers in
>> this particular case) are available makes this especially problematic.
>> Bounce buffering, unlike what the PR synopsis would suggest, works
>> fine.
>> 
>> While on the subject, properly implement swi_vm().
> 
> NIC drivers do not handle deferred load operations at all (note that 
> bus_dmamap_load_mbuf() and bus_dmamap_load_mbuf_sg() enforce BUS_DMA_NOWAIT).
> It is common practice to just drop the packet in that case.
> 

Yes, long ago when network drivers started being converted to busdma, it was agreed that EINPROGRESS simply doesn't make sense for them.  Any platform that winds up making extensive use of bounce buffers for network hardware is going to perform poorly no matter what, and should hopefully have some sort of IOMMU that can be used instead.

Scott