From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262139AbTLNRRX (ORCPT ); Sun, 14 Dec 2003 12:17:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262181AbTLNRRX (ORCPT ); Sun, 14 Dec 2003 12:17:23 -0500 Received: from mail.jlokier.co.uk ([81.29.64.88]:21636 "EHLO mail.shareable.org") by vger.kernel.org with ESMTP id S262139AbTLNRRW (ORCPT ); Sun, 14 Dec 2003 12:17:22 -0500 Date: Sun, 14 Dec 2003 17:16:37 +0000 From: Jamie Lokier To: Peter Horton Cc: Linus Torvalds , linux-mips@linux-mips.org, linux-kernel@vger.kernel.org Subject: Re: Possible shared mapping bug in 2.4.23 (at least MIPS/Sparc) Message-ID: <20031214171637.GA28923@mail.shareable.org> References: <20031213114134.GA9896@skeleton-jack> <20031213222626.GA20153@mail.shareable.org> <20031214103803.GA916@skeleton-jack> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20031214103803.GA916@skeleton-jack> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Peter Horton wrote: > I've seen code written for X86 use MAP_FIXED to create self wrapping > ring buffers. Surely it's better to fail the mmap() on other archs > rather than for the code to fail in unexpected ways? Such code should test the buffers or just not create ring buffers on architectures it doesn't know about. (You can usually simulate them by copying data). On some architectures there is _no_ alignment which works, and even on x86 aligning aliases to 32k results in faster memory accesses on some chips (AMD ones). Also, sometimes a self wrapping ring buffer can work even when the separation isn't coherent, provided the code using it forces cache line flushes at the appropriate points. -- Jamie