On Mon, Mar 29, 1999 at 01:44:53AM -0800, Don Lewis wrote:
> On Mar 26, 11:11pm, "Brian C. Grayson" wrote:
> } Subject: Re: softdep?
> 
> }   Here's my pipe-dream reason for the question:
> }   I've wondered what performance would be like if one made a
> } homebrew NVRAM (sitting on a parallel port or ISA, rather than
> } PCI or a SIMM slot) and changed all FFS mounts to be async --
> 
> I suspect that parallel port would be too slow and even ISA would
> hurt performance.  Many (most?) disk writes would need to update
> NVRAM.  Ideally the NVRAM should be close to main memory speed.

I don't think ISA would be too bad for speed reasons, all you have to do
is beat the latency of a disk drive and it should be a win. However, I 
think PCI is important for another reason. I suspect it would be desirable
to do DMA to the NVRAM, and I don't know whether PC architechture would
let you map RAM on a card into a memory space below the top of the RAM
installed on the motherboard. Anyone with more info have an answer to
that one? 

With a PCI card you could map the NVRAM with DMA into >16Mb address
space, and I don't think any machine you want this performance boost on
is likely to have <16M of RAM eh?

-- 
David Maxwell, david@vex.net|david@maxwell.net --> Mastery of UNIX, like
mastery of language, offers real freedom. The price of freedom is always dear,
but there's no substitute. Personally, I'd rather pay for my freedom than live
in a bitmapped, pop-up-happy dungeon like NT. - Thomas Scoville