Re: [PATCH v3 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently

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On 19.07.19 02:58, Nadav Amit wrote:
To improve TLB shootdown performance, flush the remote and local TLBs
concurrently. Introduce flush_tlb_multi() that does so. Introduce
paravirtual versions of flush_tlb_multi() for KVM, Xen and hyper-v (Xen
and hyper-v are only compile-tested).

While the updated smp infrastructure is capable of running a function on
a single local core, it is not optimized for this case. The multiple
function calls and the indirect branch introduce some overhead, and
might make local TLB flushes slower than they were before the recent
changes.

Before calling the SMP infrastructure, check if only a local TLB flush
is needed to restore the lost performance in this common case. This
requires to check mm_cpumask() one more time, but unless this mask is
updated very frequently, this should impact performance negatively.

Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Sasha Levin <sashal@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: linux-hyperv@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
Cc: kvm@xxxxxxxxxxxxxxx
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
---
  arch/x86/hyperv/mmu.c                 | 10 +++---
  arch/x86/include/asm/paravirt.h       |  6 ++--
  arch/x86/include/asm/paravirt_types.h |  4 +--
  arch/x86/include/asm/tlbflush.h       |  8 ++---
  arch/x86/include/asm/trace/hyperv.h   |  2 +-
  arch/x86/kernel/kvm.c                 | 11 +++++--
  arch/x86/kernel/paravirt.c            |  2 +-
  arch/x86/mm/tlb.c                     | 47 ++++++++++++++++++---------
  arch/x86/xen/mmu_pv.c                 | 11 +++----
  include/trace/events/xen.h            |  2 +-
  10 files changed, 62 insertions(+), 41 deletions(-)

Xen and paravirt parts: Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen



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