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: <874irqywh2.fsf@DESKTOP-5N7EMDA>
Date: Thu, 23 Oct 2025 14:15:53 +0800
From: "Huang, Ying" <ying.huang@...ux.alibaba.com>
To: Barry Song <21cnbao@...il.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

Barry Song <21cnbao@...il.com> writes:

>> >
>> > 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.

Sure.  I can git it a try.  Can you share the test case?

>>
>> > 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.

---
Best Regards,
Huang, Ying