From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lxmtout1.gsi.de (lxmtout1.gsi.de [140.181.3.111]) by sourceware.org (Postfix) with ESMTPS id 7A550385DC35 for ; Wed, 23 Feb 2022 16:10:44 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 7A550385DC35 Received: from localhost (localhost [127.0.0.1]) by lxmtout1.gsi.de (Postfix) with ESMTP id CD0592051046 for ; Wed, 23 Feb 2022 17:10:42 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at lxmtout1.gsi.de Received: from lxmtout1.gsi.de ([127.0.0.1]) by localhost (lxmtout1.gsi.de [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 7GNknEsOamqF for ; Wed, 23 Feb 2022 17:10:42 +0100 (CET) Received: from srvex3.campus.gsi.de (unknown [10.10.4.16]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-SHA256 (128/128 bits)) (No client certificate requested) by lxmtout1.gsi.de (Postfix) with ESMTPS id B5AC42051045 for ; Wed, 23 Feb 2022 17:10:42 +0100 (CET) Received: from srvex1.Campus.gsi.de (10.10.4.11) by srvex3.campus.gsi.de (10.10.4.16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2375.18; Wed, 23 Feb 2022 17:10:42 +0100 Received: from srvex1.Campus.gsi.de ([fe80::d6d:62f8:8c5f:1743]) by srvex1.campus.gsi.de ([fe80::d6d:62f8:8c5f:1743%21]) with mapi id 15.01.2375.018; Wed, 23 Feb 2022 17:10:42 +0100 From: "Bertini, Denis Dr." To: "fortran@gcc.gnu.org" Subject: Problem setting buffer size for gfortran ( v 11.2) Thread-Topic: Problem setting buffer size for gfortran ( v 11.2) Thread-Index: AQHYKM6M27OpBPwmgkOLiZTs/UPI8Q== Date: Wed, 23 Feb 2022 16:10:42 +0000 Message-ID: Accept-Language: en-US, de-DE Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [140.181.3.12] MIME-Version: 1.0 X-Spam-Status: No, score=-0.7 required=5.0 tests=BAYES_50, HTML_MESSAGE, KAM_DMARC_STATUS, SPF_HELO_PASS, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: fortran@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Fortran mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 23 Feb 2022 16:10:46 -0000 Hi Investigating some sporadical performance drop when using Fortran IO on our= Lustre shared file system, we realized that the buffer size used as default by the= gnu fortran compiler is 8 kiB only. We wanted to change this default and according to the documentation, one ha= s just to set the environment variables: GFORTRAN_UNFORMATTED_BUFFER_SIZE GFORTRAN_FORMATTED_BUFFER_SIZE=3D GFORTRAN_UNBUFFERED_ALL=3Dn to increase the buffer size during runtime. Unfortunately isetting these variables does not change the default buffer= size. I tried with gfortran 8, 10, and the new 11.2. Looking a the code, i found in io/unix.c that the default is set to the following value, static const int FORMATTED_BUFFER_SIZE_DEFAULT =3D 8192; static const int UNFORMATTED_BUFFER_SIZE_DEFAULT =3D 128*1024; Of course, changing the default value and recompiling works and change acco= rdingly the buffer size It should nevertheless be possible to change these values without recompili= ng. Is there something one should be aware of when setting these variables? Best regards, Denis --------- Denis Bertini Abteilung: CIT Ort: SB3 2.265a Tel: +49 6159 71 2240 Fax: +49 6159 71 2986 E-Mail: d.bertini@gsi.de GSI Helmholtzzentrum f=FCr Schwerionenforschung GmbH Planckstra=DFe 1, 64291 Darmstadt, Germany, www.gsi.de Commercial Register / Handelsregister: Amtsgericht Darmstadt, HRB 1528 Managing Directors / Gesch=E4ftsf=FChrung: Professor Dr. Paolo Giubellino, Dr. Ulrich Breuer, J=F6rg Blaurock Chairman of the GSI Supervisory Board / Vorsitzender des GSI-Aufsichtsrats: Ministerialdirigent Dr. Volkmar Dietz