* Andi Kleen <[EMAIL PROTECTED]> wrote:
> > What is very real though are the hard limitations of MTRRs. So i'd
> > rather first like to see a clean PAT approach (which all other
> > modern OSs have already migrated to in the past 10 years)
>
> That's mostly orthogonal. Don't know why you bring it up now?
because the PAT (Page Attribute Table support) patchset and the CPA
(change_page_attr()) patchset are are not orthogonal at all - as their
name already signals: because they change the implementation/effects of
the same interface(s). [just at different levels].
Both patchsets change how the kernel pagetable caching is handled. PAT
changes the kernel pte details and unshackles us from MTRR reliance and
thus solves real problems on real boxes:
55 files changed, 1288 insertions(+), 237 deletions(-)
CPA moves change_page_attr() from invwb flushing to cflush flushing, for
a speedup/latency-win, plus a whole bunch of intermingled fixes and
improvements to page attribute modification:
26 files changed, 882 insertions(+), 423 deletions(-)
so in terms of risk management, the "perfect patch order" is:
- minimal_set of correctness fixes to the highlevel cpa code.
- ( then any provably NOP cleanups to pave the way. )
- then change the lowlevel pte code (PAT) to reduce/eliminate the need
to have runtime MTRR use
- then structural improvements/cleanups of the highlevel cpa code
- then the cflush (optional) performance feature ontop of it.
- then gigabyte-largepages/TLBs support [new CPU feature that further
complicates page-attribute management]
All in an easy-to-revert fashion. We _will_ regress here, and this stuff
is very hard to debug.
Ingo
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