Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261190AbTEEKAC (ORCPT ); Mon, 5 May 2003 06:00:02 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261199AbTEEKAC (ORCPT ); Mon, 5 May 2003 06:00:02 -0400 Received: from elin.scali.no ([62.70.89.10]:61571 "EHLO elin.scali.no") by vger.kernel.org with ESMTP id S261190AbTEEKAA (ORCPT ); Mon, 5 May 2003 06:00:00 -0400 Subject: Re: The disappearing sys_call_table export. From: Terje Eggestad To: Arjan van de Ven Cc: Christoph Hellwig , linux-kernel , D.A.Fedorov@inp.nsk.su In-Reply-To: <20030505093810.A22327@devserv.devel.redhat.com> References: <1052122784.2821.4.camel@pc-16.office.scali.no> <20030505092324.A13336@infradead.org> <1052127216.2821.51.camel@pc-16.office.scali.no> <20030505093810.A22327@devserv.devel.redhat.com> Content-Type: text/plain Organization: Scali AS Message-Id: <1052129543.2821.87.camel@pc-16.office.scali.no> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.2.2 (1.2.2-4) Date: 05 May 2003 12:12:23 +0200 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1760 Lines: 58 On Mon, 2003-05-05 at 11:38, Arjan van de Ven wrote: > On Mon, May 05, 2003 at 11:33:36AM +0200, Terje Eggestad wrote: > > 1. performance is everything. > > 2. We're making a MPI library, and as such we don't have any control > > with the application. > > 3a. The various hardware for cluster interconnect all work with DMA. > > 3b. the performance loss from copying from a receive area to the > > userspace buffer is unacceptable. > > 3c. It's therefore necessary for HW to access user pages. > > 4. In order to to 3, the user pages must be pinned down. > > see how AIO does this, and O_DIRECT, and rawio. > > They all have the same requirement and manage to cope. Ok, I havn't actually checked the code , but no, they don't have the same requirement. they pin and unpin the user space memory at the beginning and and of the operations. take aio pseudo code: aio_write() { pinmem(); if (file) add_write_to_disk_queue(); . . . }; kernel_aio_completion_handler() { unpinmem(); send_completion_event_to_task(); }; -- _________________________________________________________________________ Terje Eggestad mailto:terje.eggestad@scali.no Scali Scalable Linux Systems http://www.scali.com Olaf Helsets Vei 6 tel: +47 22 62 89 61 (OFFICE) P.O.Box 150, Oppsal +47 975 31 574 (MOBILE) N-0619 Oslo fax: +47 22 62 89 51 NORWAY _________________________________________________________________________ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/