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

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Message-ID: <CALCETrUicyG0NJfj309zU6SX1Xdq6gcmC9+zGLqW4iFkodnWjw@mail.gmail.com>
Date:   Tue, 25 Jun 2019 20:51:05 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Nadav Amit <namit@...are.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        Linux Virtualization <virtualization@...ts.linux-foundation.org>,
        kvm list <kvm@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 4/9] x86/mm/tlb: Flush remote and local TLBs concurrently

On Tue, Jun 25, 2019 at 8:48 PM Nadav Amit <namit@...are.com> wrote:
>
> > On Jun 25, 2019, at 8:36 PM, Andy Lutomirski <luto@...nel.org> wrote:
> >
> > On Wed, Jun 12, 2019 at 11:49 PM Nadav Amit <namit@...are.com> wrote:
> >> To improve TLB shootdown performance, flush the remote and local TLBs
> >> concurrently. Introduce flush_tlb_multi() that does so. The current
> >> flush_tlb_others() interface is kept, since paravirtual interfaces need
> >> to be adapted first before it can be removed. This is left for future
> >> work. In such PV environments, TLB flushes are not performed, at this
> >> time, concurrently.
> >
> > Would it be straightforward to have a default PV flush_tlb_multi()
> > that uses flush_tlb_others() under the hood?
>
> I prefer not to have a default PV implementation that should anyhow go away.
>
> I can create unoptimized untested versions for Xen and Hyper-V, if you want.
>

I think I prefer that approach.  We should be able to get the
maintainers to test it.  I don't love having legacy paths in there,
ahem, UV.