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

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Date:   Fri, 26 Jul 2019 09:28:01 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Nadav Amit <namit@...are.com>, Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/9] x86/mm/tlb: Flush remote and local TLBs
 concurrently

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@...rosoft.com>
> Cc: Haiyang Zhang <haiyangz@...rosoft.com>
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: Sasha Levin <sashal@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: x86@...nel.org
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: linux-hyperv@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Cc: virtualization@...ts.linux-foundation.org
> Cc: kvm@...r.kernel.org
> Cc: xen-devel@...ts.xenproject.org
> Signed-off-by: Nadav Amit <namit@...are.com>
> ---
>   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@...e.com>


Juergen