From mboxrd@z Thu Jan 1 00:00:00 1970 From: Werner Almesberger Subject: barriers vs. reads Date: Tue, 22 Jun 2004 00:53:02 -0300 Sender: linux-fsdevel-owner@vger.kernel.org Message-ID: <20040622005302.A1325@almesberger.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from almesberger.net ([63.105.73.238]:13321 "EHLO host.almesberger.net") by vger.kernel.org with ESMTP id S266551AbUFVDxX (ORCPT ); Mon, 21 Jun 2004 23:53:23 -0400 Received: from almesberger.net (vpnwa-home [10.200.0.2]) by host.almesberger.net (8.11.6/8.9.3) with ESMTP id i5M3rH423329 for ; Mon, 21 Jun 2004 20:53:17 -0700 Received: (from werner@localhost) by almesberger.net (8.11.6/8.11.6) id i5M3r2824415 for linux-fsdevel@vger.kernel.org; Tue, 22 Jun 2004 00:53:02 -0300 To: linux-fsdevel@vger.kernel.org Content-Disposition: inline List-Id: linux-fsdevel.vger.kernel.org I'm working on an elevator with priorities, and I'm wondering what semantics are expected from barriers when it comes to reads. My problem with read barriers is that they can upset priorities quite a bit, by forcing the entire queue to be processed before any new (possibly timing-critical) reads are allowed. So, is there anything that actually depends on barriers also constraining read - or, more likely, read vs. write - order ? If not, will there be ? Also, it seems, but is never quite explicitly spelt out, that an elevator is never really supposed to look for barriers in rq->flags, but can solely rely on the insertion position as an indication for barriers. Is this true ? Thanks, - Werner -- _________________________________________________________________________ / Werner Almesberger, Buenos Aires, Argentina wa@almesberger.net / /_http://www.almesberger.net/____________________________________________/