linux-kernel - Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault

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Message-ID: <CAGsJ_4z7SASir4gWThfePdnvw82TB8E6rXnzJ=CieaFnJpJt7g@mail.gmail.com>
Date: Thu, 23 Oct 2025 18:39:39 +1300
From: Barry Song <21cnbao@...il.com>
To: "Huang, Ying" <ying.huang@...ux.alibaba.com>
Cc: Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, 
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Zi Yan <ziy@...dia.com>, 
	Baolin Wang <baolin.wang@...ux.alibaba.com>, Ryan Roberts <ryan.roberts@....com>, 
	Yang Shi <yang@...amperecomputing.com>, "Christoph Lameter (Ampere)" <cl@...two.org>, Dev Jain <dev.jain@....com>, 
	Anshuman Khandual <anshuman.khandual@....com>, Yicong Yang <yangyicong@...ilicon.com>, 
	Kefeng Wang <wangkefeng.wang@...wei.com>, Kevin Brodsky <kevin.brodsky@....com>, 
	Yin Fengwei <fengwei_yin@...ux.alibaba.com>, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page
 reused in write fault

> >
> > A:
> > write pte
> > don't broadcast pte
> > tlbi
> > don't broadcast tlbi
> >
> > with
> >
> > B:
> > write pte
> > broadcast pte
>
> I suspect that pte will be broadcast, DVM broadcast isn't used for
> the memory coherency IIUC.

I guess you’re right. By “broadcast,” I actually meant the PTE becoming visible
to other CPUs. With a dsb(ish) before tlbi, other cores’ TLBs can load the new
PTE after their TLB is shoot down. But as you said, if the hardware doesn’t
propagate the updated PTE faster, it doesn’t seem to help reduce page faults.

As a side note, I’m curious about the data between dsb(nsh) and dsb(ish) on
your platform. Perhaps because the number of CPU cores is small, I didn’t see
any noticeable difference between them on phones.

>
> > tlbi
> > don't broadcast tlbi
> >
> > I guess the gain comes from "don't broadcat tlbi" ?
> > With B, we should be able to share many existing code.
>
> Ryan has some plan to reduce the code duplication with the current
> solution.

Ok.

Thanks
Barry