[PATCH v3 0/8] KVM paravirt remote flush tlb

["Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>]

Remote flushing api's does a busy wait which is fine in bare-metal
scenario. But with-in the guest, the vcpus might have been pre-empted
or blocked. In this scenario, the initator vcpu would end up
busy-waiting for a long amount of time.

This was discovered in our gang scheduling test and other way to solve
this is by para-virtualizing the flush_tlb_others_ipi(now shows up as
smp_call_function_many after Alex Shi's TLB optimization)

This patch set implements para-virt flush tlbs making sure that it
does not wait for vcpus that are sleeping. And all the sleeping vcpus
flush the tlb on guest enter. Idea was discussed here:
https://lkml.org/lkml/2012/2/20/157

This also brings one more dependency for lock-less page walk that is
performed by get_user_pages_fast(gup_fast). gup_fast disables the
interrupt and assumes that the pages will not be freed during that
period. And this was fine as the flush_tlb_others_ipi would wait for
all the IPI to be processed and return back. With the new approach of
not waiting for the sleeping vcpus, this assumption is not valid
anymore. So now HAVE_RCU_TABLE_FREE is used to free the pages. This
will make sure that all the cpus would atleast process smp_callback
before the pages are freed.

Changelog from v2:
• Rebase to 3.5 based linus(commit - f7da9cd) kernel.
• Port PV-Flush to new TLB-Optimization code by Alex Shi
• Use pinned pages to avoid overhead during guest enter/exit (Marcelo)
• Remove kick, as this is not improving much
• Use bit fields in the state(flush_on_enter and vcpu_running) flag to
  avoid smp barriers (Marcelo)
• Add documentation for Paravirt TLB Flush (Marcelo)

Changelog from v1:
• Race fixes reported by Vatsa
• Address gup_fast dependency using PeterZ's rcu table free patch
• Fix rcu_table_free for hw pagetable walkers

Here are the results from PLE hardware. Here is the setup details:
• 32 CPUs (HT disabled)
• 64-bit VM
   • 32vcpus
   • 8GB RAM

Base: f7da9cd (based on 3.5 kernel, includes rik's changes and alex
      shi's changes)
ple-opt: Raghu's PLE improvements [1](in kvm:auto-next now)
pv3flsh: ple-opt + paravirt flush v3

Lower is better
    kbench - 1VM
    ============
		Avg        Stddev
    base      16.714089     1.2471967
    pleopt    12.527411    0.15261886
    pv3flsh   12.955556     0.5041832

    kbench - 2VM
    ============
		Avg        Stddev
    base      28.565933     3.0167804
    pleopt      22.7613     1.9046476
    pv3flsh    23.034083     2.2192968

Higher is better
    ebizzy - 1VM
    ============
		Avg        Stddev
    base          1091     21.674358
    pleopt        2239     45.188494
    pv3flsh       2170.7     44.592102

    ebizzy - 2VM
    ============
		Avg        Stddev
    base         1824.7     63.708299
    pleopt       2383.2     107.46779
    pv3flsh      2328.2     69.359172

Observations:
-------------
Looking at the results above, ple-opt[1] patches have addressed the
remote-flush-tlb issue that we were trying to address using the
paravirt-tlb-flush approach. 

[1] http://article.gmane.org/gmane.linux.kernel/1329752

---

Nikunj A. Dadhania (6):
      KVM Guest: Add VCPU running/pre-empted state for guest
      KVM-HV: Add VCPU running/pre-empted state for guest
      KVM Guest: Add paravirt kvm_flush_tlb_others
      KVM-HV: Add flush_on_enter before guest enter
      Enable HAVE_RCU_TABLE_FREE for kvm when PARAVIRT_TLB_FLUSH is enabled
      KVM-doc: Add paravirt tlb flush document

Peter Zijlstra (2):
      mm, x86: Add HAVE_RCU_TABLE_FREE support
      mm: Add missing TLB invalidate to RCU page-table freeing


 Documentation/virtual/kvm/msr.txt                |    4 +
 Documentation/virtual/kvm/paravirt-tlb-flush.txt |   53 +++++++++++++++++++
 arch/Kconfig                                     |    3 +
 arch/powerpc/Kconfig                             |    1 
 arch/sparc/Kconfig                               |    1 
 arch/x86/Kconfig                                 |   11 ++++
 arch/x86/include/asm/kvm_host.h                  |    7 ++
 arch/x86/include/asm/kvm_para.h                  |   13 +++++
 arch/x86/include/asm/tlb.h                       |    1 
 arch/x86/include/asm/tlbflush.h                  |   11 ++++
 arch/x86/kernel/kvm.c                            |   38 +++++++++++++
 arch/x86/kvm/cpuid.c                             |    1 
 arch/x86/kvm/x86.c                               |   62 +++++++++++++++++++++-
 arch/x86/mm/pgtable.c                            |    6 +-
 arch/x86/mm/tlb.c                                |   37 +++++++++++++
 include/asm-generic/tlb.h                        |    9 +++
 mm/memory.c                                      |   43 +++++++++++++--
 17 files changed, 290 insertions(+), 11 deletions(-)
 create mode 100644 Documentation/virtual/kvm/paravirt-tlb-flush.txt