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Mon, 24 Feb 2025 14:08:17 -0800 (PST) Precedence: bulk X-Mailing-List: linux-input@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250223164217.2139331-1-visitorckw@gmail.com> <20250223164217.2139331-4-visitorckw@gmail.com> In-Reply-To: From: Uros Bizjak Date: Mon, 24 Feb 2025 23:08:05 +0100 X-Gm-Features: AWEUYZk0kdMcSa1NJ7f-FEs-56xLQUiW9T9ljXTGABrJPIypOLr5b30gUzs5pw0 Message-ID: Subject: Re: [PATCH 03/17] x86: Replace open-coded parity calculation with parity8() To: "H. Peter Anvin" Cc: Kuan-Wei Chiu , tglx@linutronix.de, Ingo Molnar , bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, jk@ozlabs.org, joel@jms.id.au, eajames@linux.ibm.com, andrzej.hajda@intel.com, neil.armstrong@linaro.org, rfoss@kernel.org, maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@gmail.com, simona@ffwll.ch, dmitry.torokhov@gmail.com, mchehab@kernel.org, awalls@md.metrocast.net, hverkuil@xs4all.nl, miquel.raynal@bootlin.com, richard@nod.at, vigneshr@ti.com, louis.peens@corigine.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, parthiban.veerasooran@microchip.com, arend.vanspriel@broadcom.com, johannes@sipsolutions.net, gregkh@linuxfoundation.org, jirislaby@kernel.org, yury.norov@gmail.com, akpm@linux-foundation.org, mingo@kernel.org, alistair@popple.id.au, linux@rasmusvillemoes.dk, Laurent.pinchart@ideasonboard.com, jonas@kwiboo.se, jernej.skrabec@gmail.com, kuba@kernel.org, linux-kernel@vger.kernel.org, linux-fsi@lists.ozlabs.org, dri-devel@lists.freedesktop.org, linux-input@vger.kernel.org, linux-media@vger.kernel.org, linux-mtd@lists.infradead.org, oss-drivers@corigine.com, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, brcm80211@lists.linux.dev, brcm80211-dev-list.pdl@broadcom.com, linux-serial@vger.kernel.org, bpf@vger.kernel.org, jserv@ccns.ncku.edu.tw, Yu-Chun Lin Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, Feb 24, 2025 at 10:56=E2=80=AFPM H. Peter Anvin wro= te: > > On 2/24/25 07:24, Uros Bizjak wrote: > > > > > > On 23. 02. 25 17:42, Kuan-Wei Chiu wrote: > >> Refactor parity calculations to use the standard parity8() helper. Thi= s > >> change eliminates redundant implementations and improves code > >> efficiency. > > > > The patch improves parity assembly code in bootflag.o from: > > > > 58: 89 de mov %ebx,%esi > > 5a: b9 08 00 00 00 mov $0x8,%ecx > > 5f: 31 d2 xor %edx,%edx > > 61: 89 f0 mov %esi,%eax > > 63: 89 d7 mov %edx,%edi > > 65: 40 d0 ee shr %sil > > 68: 83 e0 01 and $0x1,%eax > > 6b: 31 c2 xor %eax,%edx > > 6d: 83 e9 01 sub $0x1,%ecx > > 70: 75 ef jne 61 > > 72: 39 c7 cmp %eax,%edi > > 74: 74 7f je f5 > > 76: > > > > to: > > > > 54: 89 d8 mov %ebx,%eax > > 56: ba 96 69 00 00 mov $0x6996,%edx > > 5b: c0 e8 04 shr $0x4,%al > > 5e: 31 d8 xor %ebx,%eax > > 60: 83 e0 0f and $0xf,%eax > > 63: 0f a3 c2 bt %eax,%edx > > 66: 73 64 jae cc > > 68: > > > > which is faster and smaller (-10 bytes) code. > > > > Of course, on x86, parity8() and parity16() can be implemented very simpl= y: > > (Also, the parity functions really ought to return bool, and be flagged > __attribute_const__.) > > static inline __attribute_const__ bool _arch_parity8(u8 val) > { > bool parity; > asm("and %0,%0" : "=3D@ccnp" (parity) : "q" (val)); asm("test %0,%0" : "=3D@ccnp" (parity) : "q" (val)); because we are interested only in flags. Uros.