From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) by sourceware.org (Postfix) with ESMTPS id 842253857C7E for ; Sat, 5 Dec 2020 17:46:07 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 842253857C7E Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=gmx.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=sdack@gmx.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1607190365; bh=D7Pc6hm6SvCPpYpYuWbgEcxxm0zJ+nbZe4XEXoKGgkE=; h=X-UI-Sender-Class:To:From:Subject:Date; b=b5c/C6SOkiJMh8clO9i4ktIG7QWyOhN1wOr0bXi+cfOurGdqiQBVXUnqBqEXpcUoE hUC8sinYIHzITc8aNwAG4fxeiTjVNED4xqxOak6XP9noVjhJITOdiDoVAKLKwmoo6A Qb/cDGyHJP4/Sj8ZBVJ7RD+bBiEC0L/gqRL7D9nw= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [192.168.0.2] ([2.100.248.2]) by mail.gmx.com (mrgmx004 [212.227.17.184]) with ESMTPSA (Nemesis) id 1N8ob6-1k8OiZ2etK-015rzV for ; Sat, 05 Dec 2020 18:46:05 +0100 To: gcc-help@gcc.gnu.org From: "Sven C. Dack" Subject: L1/L2 cache characteristics and -mtune=znver2 versus run-time detection Message-ID: Date: Sat, 5 Dec 2020 17:46:04 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable Content-Language: en-GB X-Provags-ID: V03:K1:ywQg193G0ItgTp+9fBLbuw5RnjUjnN0u0xdwkxvpmTGfKcRyymE TpHBd2VT+zU1XamvsEseCpBLpOV6W1L6QrTjOYf+/VQRNjRgw2jabrzELO73irhYy/Q3bwP 3Ktp9uuBepJt21NGU+8lfotp+7KN13GsA6I1xf4YY6uFvmxrOKqQvpDpklkTV5B5V3XqTR6 lnVirpT7DU94IIZUwcfcw== X-UI-Out-Filterresults: notjunk:1;V03:K0:m7hsmCH5CZk=:owcHVQKmnsxrin1BYUCR1o 47alE0He2f3XhLLt/iVdCFt5E3lpLEZpkOsd6vmIaW8i25nMKn+m3xcRMTK30kbyC01Kffs3o q8HncgiaSZHw7FDmr2/grg5p6UYZA4x3Yr1h9OwhLUltYn/cmZjE0tBTKsrUtdT7AM3MFI90p 16KJ0gZmJlKF+zQDciFULVafSZsfdsAALOtDHgnnflE5qGw0xf6z61iK5AQRfoAkTuyTCuffS K1IR9W9KfG6vaOGY/G2yxT/zJN8Wc3gMpS+QY9B4a+sL417umrnbZc5EkTEb1PQjbMz7Wd/2B CygLyjCWR0I9ue/vK3ooaF78JkueRDEoglvqFynrbo9Qov0YP5S1yo4anqTIWeLKoaHVuEq8n wYRortLhUrubCPWt+j9BSB2VCNf48WqPkYlFG21k3kbr72nrenPhi3KYYw25CN2w0xZ7fqoo6 s1K1u34B13zfmySUKh6HWvv+0WA6o/LYTJHK0OdEZ9iEX24FncE5h1A3Ae+9aY46oXuHhWEqT CmvBamESplhFTpLkYmw1ihOvbdWbc5qcflmobfkKiHxdMXe1c1/TigFyd6F7a8bjKq8vFNvZR OEsXk3lDbXNuBBO7DCAYsmdlmKCK9bT8219u/FdQLrO49XwKWwVqKSCrtxRnjJSf4IMVdr4jV OWAtQUOIkMQM+YBt7+NDtJE6ol9czxBJVLf29KbG3olcEuBqmzJ0t/v3lJx0cY/Y/KxefiEk9 hxVRmX5zEaqI5Kg64cOR45EWPOkPO2MaOCs0Z1BEpWyZ/r1JE+z/pmugHiTD6i/zm4atimW/L +TwVJ4OmqFSSUeAB7EWnRIJnU3YwNp+og8/MWm73ixLDYkvLjbs6o+XqQ9LSx0ePOTBQStOdW KJGvvomBX3fjssji4D1Q== X-Spam-Status: No, score=-1.2 required=5.0 tests=BAYES_00, BODY_8BITS, DKIM_SIGNED, DKIM_VALID, FREEMAIL_FROM, RCVD_IN_DNSWL_LOW, RCVD_IN_MSPIKE_H2, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-help@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-help mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 05 Dec 2020 17:46:10 -0000 Hello, I've come across an unexpected behaviour of gcc and wanted to ask for help. I've noticed that when I specify '-march=3Dznver2' does gcc use the incorrect values for the L1/L2 cache. Only when '-march=3Dnative' was used and gcc detected the CPU at run-time does it use the correct values. For example on a Ryzen 7 3800X (a Zen 2 CPU): $ gcc -march=3Dznver2 --help=3Dparams -Q|fgrep cache =C2=A0 --param=3Dl1-cache-line-size=3D =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 32 =C2=A0 --param=3Dl1-cache-size=3D=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 64 =C2=A0 --param=3Dl2-cache-size=3D=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 512 versus: $ gcc -march=3Dnative --help=3Dparams -Q|fgrep cache =C2=A0 --param=3Dl1-cache-line-size=3D =C2=A0=C2=A0=C2=A0 =C2=A0=C2=A0=C2= =A0 64 =C2=A0 --param=3Dl1-cache-size=3D=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 32 =C2=A0 --param=3Dl2-cache-size=3D=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 512 GCC does detect the CPU as 'znver2': $ gcc -march=3Dnative --help=3Dtarget -Q|fgrep march =C2=A0 -march=3D=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 =C2=A0=C2= =A0=C2=A0 =C2=A0=C2=A0=C2=A0 znver2 I've also verified this behaviour with '-mtune=3Dznver2', and again does GCC only use the correct values when it uses auto-detection. Why does GCC not use the correct L1/L2 cache values when '-march=3Dznver2' or '-mtune=3Dznver2' is specified? Sven