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Wed, 22 Oct 2025 17:46:49 +0800 From: "Huang, Ying" To: Barry Song <21cnbao@gmail.com> Cc: Catalin Marinas , Will Deacon , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Vlastimil Babka , Zi Yan , Baolin Wang , Ryan Roberts , Yang Shi , "Christoph Lameter (Ampere)" , Dev Jain , Anshuman Khandual , Yicong Yang , Kefeng Wang , Kevin Brodsky , Yin Fengwei , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH -v2 2/2] arm64, tlbflush: don't TLBI broadcast if page reused in write fault In-Reply-To: (Barry Song's message of "Wed, 22 Oct 2025 22:37:54 +1300") References: <20251013092038.6963-1-ying.huang@linux.alibaba.com> <20251013092038.6963-3-ying.huang@linux.alibaba.com> <87a51jfl44.fsf@DESKTOP-5N7EMDA> <871pmv9unr.fsf@DESKTOP-5N7EMDA> <875xc78es0.fsf@DESKTOP-5N7EMDA> Date: Wed, 22 Oct 2025 17:46:48 +0800 Message-ID: <87a51j6zg7.fsf@DESKTOP-5N7EMDA> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D5F73C000C X-Stat-Signature: y8u3iic1yhri4sodqjzhmaqgijxtc74f X-HE-Tag: 1761126414-693808 X-HE-Meta: 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 iFxIOJKJ Ouq4CgmZzv5cNLYa7NtE5txOLtZbVxG808yz3IbyL6ce+W53EOJLT7AR7vOEr7tyf1xuAKyxxBY8ZBrO7TyR1ZHMTG6iJAERFw6006/vf4gGB0hRc1EAjsnEIPOzMMrIfAR7OyDErHI9VhUEs7NAGHN1N9uMgaV3gsH8Tlo9h5rfpbhX6pEdg33Ql+5er+1znmwMMgeSynP30Re+mfDnethyTP3Yupfd6Ex1ynXVav5CcN6EDmTaxMtL3NBj80HX+hFJ8qv6dMMAlnf06ZRhJmHA3C1LBDXtKlGBn+5BLFZfdeKY= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Barry Song <21cnbao@gmail.com> writes: >> >> With PTL, this becomes >> >> CPU0: CPU1: >> >> page fault page fault >> lock PTL >> write PTE >> do local tlbi >> unlock PTL >> lock PTL <- pte visible to CPU 1 >> read PTE <- new PTE >> do local tlbi <- new PTE >> unlock PTL > > I agree. Yet the ish barrier can still avoid the page faults during CPU0's PTL. IIUC, you think that dsb(ish) compared with dsb(nsh) can accelerate memory writing (visible to other CPUs). TBH, I suspect that this is the case. > CPU0: CPU1: > > lock PTL > > write pte; > Issue ish barrier > do local tlbi; > > > No page fault occurs if tlb misses > > > unlock PTL > > > Otherwise, it could be: > > > CPU0: CPU1: > > lock PTL > > write pte; > Issue nsh barrier > do local tlbi; > > > page fault occurs if tlb misses > > > unlock PTL > > > Not quite sure if adding an ish right after the PTE modification has any > noticeable performance impact on the test? I assume the most expensive part > is still the tlbi broadcast dsb, not the PTE memory sync barrier? --- Best Regards, Huang, Ying