linux-kernel - Re: [tip:x86/mm] x86/mm/tlb: Make lazy TLB mode lazier

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Message-ID: <20180718182359.GW2494@hirez.programming.kicks-ass.net>
Date:   Wed, 18 Jul 2018 20:23:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rik van Riel <riel@...riel.com>
Cc:     songliubraving@...com, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, hpa@...or.com, tglx@...utronix.de,
        mingo@...nel.org, torvalds@...ux-foundation.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mm] x86/mm/tlb: Make lazy TLB mode lazier

On Wed, Jul 18, 2018 at 01:22:19PM -0400, Rik van Riel wrote:
> > On Jul 18, 2018, at 12:00 PM, Peter Zijlstra <peterz@...radead.org> wrote:

> > Also, I don't suppose you've looked at the paravirt instances of
> > flush_tlb_other() ? They don't elide the flushes because of lazy.
> 
> Let me look at those now :)

<snip xen>

> kvm_flush_tlb_other takes out preempted VCPUs from the flush mask, 
> before calling native_flush_tlb_others, so it should get the optimization 
> automatically.

Ah, ok. I wasn't entirely sure the new lazy was purely for the idle
case. But yes, the KVM paravirt thing should get the idle case right.

> Hyperv does ... sad magic.

Yeah,.. it got us to switch to 'rcu' freeing of page-tables and enabled
the kvm thing though, so that all is good :-)