On 11/03/17 10:15 -0400, Mikulas Patocka wrote:
>
>
> On Tue, 31 Oct 2017, Haozhong Zhang wrote:
>
> > [I just copy the commit message from patch 2]
> >
> > Some reserved pages, such as those from NVDIMM DAX devices, are
> > not for MMIO, and can be mapped with cached memory type for better
> > performance. However, the above check misconceives those pages as
>
> Note that cached memory type on persistent memory has horrible
> performance. The clwb instruction on Broadwell is very slow - when you
> write to persistent memory and use clwb to flush cache, the performance is
> about 350MB/s.
Wasn't clwb first introduced on Skylake?
Haozhong
>
> Using write-combining memory type for persistent memory is much faster, it
> can sustain performance of one 8-byte write per tick.
>
> Mikulas
>
> > MMIO. Because KVM maps MMIO pages with UC memory type, the
> > performance of guest accesses to those pages would be harmed.
> > Therefore, we check the host memory type by lookup_memtype() in
> > addition and only treat UC/UC- pages as MMIO.
> >
> > Changes in v2:
> > * Switch to lookup_memtype() to get host memory type.
> > * Rewrite the comment in KVM MMU patch.
> > * Remove v1 patch 2, which is not necessary in v2.
> >
> > Haozhong Zhang (2):
> > x86/mm: expose lookup_memtype()
> > KVM: MMU: consider host cache mode in MMIO page check
> >
> > arch/x86/include/asm/pat.h | 2 ++
> > arch/x86/kvm/mmu.c | 30 +++++++++++++++++++++++++++---
> > arch/x86/mm/pat.c | 3 ++-
> > 3 files changed, 31 insertions(+), 4 deletions(-)
> >
> > --
> > 2.14.1
> >
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