Re: Is the Scratchpad Implementation Using a LUT Standard?

[Logan Gunthorpe <lsgunthorpe@gmail.com>]

On 11/10/17 11:41 AM, Serge Semin wrote:

> You are mistaken. IDT PCIe switch have LUT. There are 24 of them available at
> the current hardware for each NTB. All of them are available to be used over
> IDT NTB driver as well as all MWs with direct address translation.
> Additionally It is true to say about just one LUT entry usage per peer, only if
> you got just two NTB-ports available per device. What if you got eight or even more
> of them? In this case you'd need to have as many LUT entries reserved as there are
> peers available to have connections to. In this case reservation doesn't seem so
> inexpensive. As far as I can see from the switchtec brief documents, there can be
> up to 48 NTBs per device. So in this case we'd loose 48 MWs just to have some
> stupid scratchpads, which is, according to your words, a third part of all the LUT
> MWs available to a port.
Ah, fair, I wasn't aware the IDT had LUT support. Using up a third of 
the LUT windows
does not seem like a problem at all considering we have no other use for 
them.
Note: the switchtec code also used the shared_mw for link management, 
not just
providing scratchpads. But once the upper layers are reworked to not 
require
scratchpads I'd be fine with removing them from the shared_mw.

Logan