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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43d8fbc12bbsm97991905e9.13.2025.03.30.11.15.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 30 Mar 2025 11:15:45 -0700 (PDT) Date: Sun, 30 Mar 2025 19:15:44 +0100 From: David Laight To: Uros Bizjak Cc: Ingo Molnar , x86@kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Subject: Re: [PATCH -tip 2/2] x86/hweight: Use POPCNT when available with X86_NATIVE_CPU option Message-ID: <20250330191544.213e07d8@pumpkin> In-Reply-To: References: <20250325164854.199420-1-ubizjak@gmail.com> <20250325164854.199420-2-ubizjak@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sun, 30 Mar 2025 18:07:30 +0200 Uros Bizjak wrote: ... > The kernel is currently compiled with -mno-red-zone, gcc-15 introduces > special "redzone" clobber to disable red-zone in the function that > includes asm() when/if the kernel starts using redzone. I really don't understand the point of a stack 'red-zone'. In any function that contains memory writes the cost of a 'sub $n,%rsp' at the top and corresponding add at the bottom is surely noise. David.