linux-kernel - Re: [RFC PATCH 5/6] x86/mm/tlb: Flush remote and local TLBs concurrently

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Message-ID: <F9875905-7383-4815-B6F6-B3EA73B7BF3F@vmware.com>
Date:   Sat, 25 May 2019 08:38:05 +0000
From:   Nadav Amit <namit@...are.com>
To:     Nadav Amit <namit@...are.com>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "x86@...nel.org" <x86@...nel.org>, Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [RFC PATCH 5/6] x86/mm/tlb: Flush remote and local TLBs
 concurrently

> On May 25, 2019, at 1:22 AM, 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.
> 
> +void native_flush_tlb_multi(const struct cpumask *cpumask,
> +			    const struct flush_tlb_info *info)
> {
> +	/*
> +	 * native_flush_tlb_multi() can handle a single CPU, but it is
> +	 * suboptimal if the local TLB should be flushed, and therefore should
> +	 * not be used in such case. Check that it is not used in such case,
> +	 * and use this assumption for tracing and accounting of remote TLB
> +	 * flushes.
> +	 */
> +	VM_WARN_ON(!cpumask_any_but(cpumask, smp_processor_id()));

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