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

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Date:   Wed, 18 Jul 2018 14:51:45 -0400
From:   Rik van Riel <riel@...riel.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 Jul 18, 2018, at 2:23 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> 
> 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.
> 
Not just idle, but also running in kernel threads like ksoftirqd,
kworker, kswapd, etc. However, kvm_flush_tlb_other calls
native_flush_tlb_other, so it should get that optimization automatically
from my patch series.