About XHCI_TD_PAGE_SIZE.

[Hans Petter Selasky]

On 12/22/14 10:31, Kohji Okuno wrote:
> In an optimisation, we should reduce the number of LINK_TRB, too.
> I heard  from a LSI engineer that,
> Generally xhci controler has the cache of TRB array. But, LINK_TRB
> may make the cache miss.

Hi,

One reason for the additional link TRB's is that I think there is 
different behaviour among the XHCI implementations how and when they 
generate a completion event. Any changes we make in that area needs to 
be tested with different XHCI controllers.

Currently only the umass driver will use transfers greater than 64KBytes 
in case of USB 3.0. Else the most common case is transfers below 
64KBytes, except for custom apps.

I have another idea pending, which is related to performance, but not 
the XHCI. I was thinking that the FreeBSD libusb could be extended to 
allocate a data buffer in the kernel which then gets mmapped to 
userspace, to save copying/copyout of USB transfer data. The problem 
about mmap() is that the buffers cannot be freed afterwards, and must 
remain in the kernel.

What do you think?

--HPS