[PATCH 0/6] x86: reduce paravirtualized spinlock overhead

Juergen Gross
Thu, 30 Apr 2015 10:53:57 -0000

Paravirtualized spinlocks produce some overhead even if the kernel is
running on bare metal. The main reason are the more complex locking
and unlocking functions. Especially unlocking is no longer just one
instruction but so complex that it is no longer inlined.

This patch series addresses this issue by adding two more pvops
functions to reduce the size of the inlined spinlock functions. When
running on bare metal unlocking is again basically one instruction.

Compile tested with CONFIG_PARAVIRT_SPINLOCKS on and off, 32 and 64
bits.

Functional testing on bare metal and as Xen dom0.

Correct patching verified by disassembly of active kernel.

Juergen Gross (6):
  x86: use macro instead of "0" for setting TICKET_SLOWPATH_FLAG
  x86: move decision about clearing slowpath flag into arch_spin_lock()
  x86: introduce new pvops function clear_slowpath
  x86: introduce new pvops function spin_unlock
  x86: switch config from UNINLINE_SPIN_UNLOCK to INLINE_SPIN_UNLOCK
  x86: remove no longer needed paravirt_ticketlocks_enabled

 arch/x86/Kconfig                      |  1 -
 arch/x86/include/asm/paravirt.h       | 13 +++++++++
 arch/x86/include/asm/paravirt_types.h | 12 ++++++++
 arch/x86/include/asm/spinlock.h       | 53 ++++++++++++-----------------------
 arch/x86/include/asm/spinlock_types.h |  3 +-
 arch/x86/kernel/kvm.c                 | 14 +--------
 arch/x86/kernel/paravirt-spinlocks.c  | 42 +++++++++++++++++++++++++--
 arch/x86/kernel/paravirt.c            | 12 ++++++++
 arch/x86/kernel/paravirt_patch_32.c   | 25 +++++++++++++++++
 arch/x86/kernel/paravirt_patch_64.c   | 24 ++++++++++++++++
 arch/x86/xen/spinlock.c               | 23 +--------------
 include/linux/spinlock_api_smp.h      |  2 +-
 kernel/Kconfig.locks                  |  7 +++--
 kernel/Kconfig.preempt                |  3 +-
 kernel/locking/spinlock.c             |  2 +-
 lib/Kconfig.debug                     |  1 -
 16 files changed, 154 insertions(+), 83 deletions(-)

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2.1.4