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Mon, 6 Feb 2023 08:20:25 -0500 (EST) X-Mailer: MessagingEngine.com Webmail Interface User-Agent: Cyrus-JMAP/3.9.0-alpha0-108-ge995779fee-fm-20230203.001-ge995779f Mime-Version: 1.0 Message-Id: <86c8ba70-2a2f-4c5b-8e74-20e3823e2db3@app.fastmail.com> In-Reply-To: References: <20230202145030.223740842@infradead.org> <20230202152655.494373332@infradead.org> <24007667-1ff3-4c86-9c17-a361c3f9f072@app.fastmail.com> Date: Mon, 06 Feb 2023 14:20:06 +0100 From: "Arnd Bergmann" To: "Peter Zijlstra" Cc: "Linus Torvalds" , "Jonathan Corbet" , "Will Deacon" , "Boqun Feng" , "Mark Rutland" , "Catalin Marinas" , dennis@kernel.org, "Tejun Heo" , "Christoph Lameter" , "Heiko Carstens" , gor@linux.ibm.com, "Alexander Gordeev" , borntraeger@linux.ibm.com, "Sven Schnelle" , "Thomas Gleixner" , "Ingo Molnar" , "Borislav Petkov" , "Dave Hansen" , x86@kernel.org, "H. Peter Anvin" , "Joerg Roedel" , suravee.suthikulpanit@amd.com, "Robin Murphy" , dwmw2@infradead.org, "Baolu Lu" , "Herbert Xu" , "David S . Miller" , "Pekka Enberg" , "David Rientjes" , "Joonsoo Kim" , "Andrew Morton" , "Vlastimil Babka" , "Roman Gushchin" , "Hyeonggon Yoo" <42.hyeyoo@gmail.com>, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-s390@vger.kernel.org, iommu@lists.linux.dev, Linux-Arch , linux-crypto@vger.kernel.org Subject: Re: [PATCH v2 05/10] percpu: Wire up cmpxchg128 Content-Type: text/plain X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 860E014001C X-Stat-Signature: jqakg3fh88436yz6o1wbyser4c11xd1u X-HE-Tag: 1675689629-983657 X-HE-Meta: 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 0+zS/dcA qNQ02Oj3OhkOnK04UVmXIbONPbyKdzieqWGouoqWy+nwYnwQ+sdyL+K9hAOzxsFzyInIjTRMV1ifuEt16bR6mw75rwqag6ZpjzihczNLo0l07ovz4NLZots/mQXTWClxHKBbg2lfLdprTLDglevP/Qe0S6vd6V2Rl8dLapLv/N3hcXfpu0IIphmflMgea/eENIdT/AobFAf3f9j1rtZn0uhaZTEubmrGlrMBb 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: On Mon, Feb 6, 2023, at 13:48, Peter Zijlstra wrote: > On Mon, Feb 06, 2023 at 01:14:28PM +0100, Peter Zijlstra wrote: >> On Mon, Feb 06, 2023 at 12:24:00PM +0100, Peter Zijlstra wrote: >> Basically, using 64bit percpu ops on 32bit is already somewhat dangerous >> -- wiring up native cmpxchg64 support in that case seemed an >> improvement. >> >> Anyway... let me get on with doing explicit >> {raw,this}_cpu_cmpxchg{64,128}() thingies. > > I only converted x86 and didn't do the automagic downgrade... > > Opinions? I think that's much better, it keeps the interface symmetric between cmpxchg and this_cpu_cmp_cmpxchg, and makes it harder to run into the subtle corner case on old x86 CPUs. For the M486/M586/MK8/MPSC/MATOM/MCORE2 configs, I would probably want to go with a compile-time check and have most distro kernels build with at least M586TSC for 32-bit or an upgraded CONFIG_GENERIC_CPU for x86_64 that assumes cmpxchg16b (nehalem, second-geneneration k8, silverthorne, ...) in order to turn system_has_cmpxchg* into a constant value on all architectures. That can be a separate discussion though and shouldn't block your series as you just keep the current state. > -#ifdef system_has_freelist_aba > +#ifdef syste_has_freelist_aba Typo Arnd