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[216.228.125.128]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2230a01fe28sm1125415ad.100.2025.02.24.14.17.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Feb 2025 14:17:31 -0800 (PST) Date: Mon, 24 Feb 2025 17:17:29 -0500 From: Yury Norov To: "H. Peter Anvin" Cc: Uros Bizjak , 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, 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 Subject: Re: [PATCH 03/17] x86: Replace open-coded parity calculation with parity8() Message-ID: References: <20250223164217.2139331-1-visitorckw@gmail.com> <20250223164217.2139331-4-visitorckw@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250224_141734_270235_87EEB5CE X-CRM114-Status: GOOD ( 13.94 ) X-BeenThere: linux-mtd@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "linux-mtd" Errors-To: linux-mtd-bounces+linux-mtd=archiver.kernel.org@lists.infradead.org On Mon, Feb 24, 2025 at 01:55:28PM -0800, H. Peter Anvin wrote: > 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. Th= is > > > change eliminates redundant implementations and improves code > > > efficiency. > > = > > The patch improves parity assembly code in bootflag.o from: > > = > > =A0 58:=A0=A0=A0 89 de=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 mov=A0=A0=A0 %ebx,%esi > > =A0 5a:=A0=A0=A0 b9 08 00 00 00=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 mov=A0= =A0=A0 $0x8,%ecx > > =A0 5f:=A0=A0=A0 31 d2=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 xor=A0=A0=A0 %edx,%edx > > =A0 61:=A0=A0=A0 89 f0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 mov=A0=A0=A0 %esi,%eax > > =A0 63:=A0=A0=A0 89 d7=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 mov=A0=A0=A0 %edx,%edi > > =A0 65:=A0=A0=A0 40 d0 ee=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 shr=A0=A0=A0 %sil > > =A0 68:=A0=A0=A0 83 e0 01=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 and=A0=A0=A0 $0x1,%eax > > =A0 6b:=A0=A0=A0 31 c2=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 xor=A0=A0=A0 %eax,%edx > > =A0 6d:=A0=A0=A0 83 e9 01=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 sub=A0=A0=A0 $0x1,%ecx > > =A0 70:=A0=A0=A0 75 ef=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 jne=A0=A0=A0 61 > > =A0 72:=A0=A0=A0 39 c7=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 cmp=A0=A0=A0 %eax,%edi > > =A0 74:=A0=A0=A0 74 7f=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 je=A0=A0=A0=A0 f5 > > =A0 76: > > = > > to: > > = > > =A0 54:=A0=A0=A0 89 d8=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 mov=A0=A0=A0 %ebx,%eax > > =A0 56:=A0=A0=A0 ba 96 69 00 00=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 mov=A0= =A0=A0 $0x6996,%edx > > =A0 5b:=A0=A0=A0 c0 e8 04=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 shr=A0=A0=A0 $0x4,%al > > =A0 5e:=A0=A0=A0 31 d8=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 xor=A0=A0=A0 %ebx,%eax > > =A0 60:=A0=A0=A0 83 e0 0f=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 and=A0=A0=A0 $0xf,%eax > > =A0 63:=A0=A0=A0 0f a3 c2=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0 bt=A0=A0=A0=A0 %eax,%edx > > =A0 66:=A0=A0=A0 73 64=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= =A0=A0=A0 jae=A0=A0=A0 cc > > =A0 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__.) There was a discussion regarding return type when parity8() was added. The integer type was taken over bool with a sort of consideration that bool should be returned as an answer to some question, like parity_odd(). To me it's not a big deal. We can switch to boolean and describe in comment what the 'true' means for the parity() function. ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/