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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4b43c748105sm5831435e9.6.2026.11.03.14.47.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Nov 2026 14:47:26 -0800 (PST) Date: Tue, 3 Nov 2026 22:47:25 +0000 From: David Laight To: "Paul E. McKenney" Cc: Jan Engelhardt , torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, Bradley Morgan , Arnd Bergmann Subject: Re: [GIT PULL] Add two-byte cmpxchg emulation function for v7.4 Message-ID: <20261103224725.253b560d@pumpkin> In-Reply-To: References: <4p5316or-75o2-s068-74s3-6q5011o75672@vanv.qr> <6f24126a-7f84-40f8-a297-095b470beb8b@paulmck-laptop> <20261102163448.3956dde3@pumpkin> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 3 Nov 2026 10:19:23 -0800 "Paul E. McKenney" wrote: > On Tue, Nov 03, 2026 at 03:03:47AM +0100, Jan Engelhardt wrote: > > > > On Monday 2026-11-02 17:34, David Laight wrote: > > >> > > >> I can get gcc-17.0.0-20261102 with no further command line options > > >> to turn `atomic_compare_exchange_strong`+uint16 into some object code > > >> that does not contain a call to libatomic, for sh2, sh3, sh4. Haven't > > >> tried xtensa or the others. > > >> Thus, is the patch really needed? > > > > > >Won't that need a big jump in the minimum supported compiler version? > > > > 12.0.0-20210420 behaves the same. I just chose 17 because that was > > convenient to try first. > > Are you also advocating ditching the single-byte cmpxchg() emulation? > If the compiler really can handle this emulation for all sizes on all > supported compilers on all affected architectures, that is actually not > at all an unattractive approach. What is the 'bloat factor'? While the function call costs, the atomic op isn't cheap either. Or are you putting the compiler generated code in the function? David > > Thanx, Paul