[PATCH v3 0/8] Improve performance of VM translation on x86_64

Alexander Duyck
2012-11-05T19:03:12Z

This patch series is meant to address several issues I encountered with VM
translations on x86_64. In my testing I found that swiotlb was incurring up
to a 5% processing overhead due to calls to __phys_addr. To address that I
have updated swiotlb to use physical addresses instead of virtual addresses
to reduce the need to call __phys_addr. However those patches didn't address
the other callers. With these patches applied I am able to achieve an
additional 1% to 2% performance gain on top of the changes to swiotlb.

The first 2 patches are the performance optimizations that result in the 1% to
2% increase in overall performance. The remaining patches are various
cleanups for a number of spots where __pa or virt_to_phys was being called
and was not needed or __pa_symbol could have been used.

It doesn't seem like the v2 patch set was accepted so I am submitting an
updated v3 set that is rebased off of linux-next with a few additional
improvements to the existing patches. Specifically the first patch now also
updates __virt_addr_valid so that it is almost identical in layout to
__phys_addr. Also I found one additional spot in init_64.c that could use
__pa_symbol instead of virt_to_page calls so I updated the first __pa_symbol
patch for the x86 init calls.

With this patch set applied I am noticing a 1-2% improvement in performance in
my routing tests. Without my earlier swiotlb changes applied it was getting as
high as 6-7% because that code originally relied heavily on virt_to_phys.

The overall effect on size varies depending on what kernel options are
enabled. I have notices that almost all of the network device drivers have
dropped in size by around 100 bytes. I suspect this is due to the fact that
the virt_to_page call in dma_map_single is now less expensive. However the
default build for x86_64 increases the vmlinux size by 3.5K with this change
applied.

---

Alexander Duyck (8):
x86/lguest: Use __pa_symbol instead of __pa on C visible symbols
x86/acpi: Use __pa_symbol instead of __pa on C visible symbols
x86/xen: Use __pa_symbol instead of __pa on C visible symbols
x86/ftrace: Use __pa_symbol instead of __pa on C visible symbols
x86: Use __pa_symbol instead of __pa on C visible symbols
x86: Drop 4 unnecessary calls to __pa_symbol
x86: Make it so that __pa_symbol can only process kernel symbols on x86_64
x86: Improve __phys_addr performance by making use of carry flags and inlining

arch/x86/include/asm/page.h | 3 +-
arch/x86/include/asm/page_32.h | 1 +
arch/x86/include/asm/page_64_types.h | 20 +++++++++++-
arch/x86/kernel/acpi/sleep.c | 2 +
arch/x86/kernel/cpu/intel.c | 2 +
arch/x86/kernel/ftrace.c | 4 +-
arch/x86/kernel/head32.c | 4 +-
arch/x86/kernel/head64.c | 4 +-
arch/x86/kernel/setup.c | 16 +++++-----
arch/x86/kernel/x8664_ksyms_64.c | 3 ++
arch/x86/lguest/boot.c | 3 +-
arch/x86/mm/init_64.c | 18 +++++------
arch/x86/mm/pageattr.c | 8 ++---
arch/x86/mm/physaddr.c | 55 +++++++++++++++++++++++++---------
arch/x86/platform/efi/efi.c | 4 +-
arch/x86/realmode/init.c | 8 ++---
arch/x86/xen/mmu.c | 21 +++++++------
17 files changed, 111 insertions(+), 65 deletions(-)

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