Re: [RFC Patch] use MTRR for write combining if PAT is not available

[Thomas Schlichter]

Konrad Rzeszutek Wilk wrote:
> I am not familiar with libpciaccess, but I was wondering why that library
> cannot realize it failed in its endeavour and use other means to accomplish
> its goals?

The thing is that the mmap() will succeed! Only the memory region will not be
set up as write combining when PAT is disabled. So userspace would have to
find out it PAT is enabled in kernel and accordingly set up MTRR entries. And
currently I don't know of a kernel interface that would tell userspace if PAT is
enabled.

Kind regards,
  Thomas
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