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

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Date:   Wed, 26 Jun 2019 03:48:49 +0000
From:   Nadav Amit <namit@...are.com>
To:     Andy Lutomirski <luto@...nel.org>
CC:     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 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.