From mboxrd@z Thu Jan 1 00:00:00 1970 From: Werner Almesberger Subject: Re: barriers vs. reads Date: Tue, 22 Jun 2004 04:50:04 -0300 Sender: linux-fsdevel-owner@vger.kernel.org Message-ID: <20040622045004.C1325@almesberger.net> References: <20040622005302.A1325@almesberger.net> <20040622073919.GV12881@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-fsdevel@vger.kernel.org Return-path: Received: from almesberger.net ([63.105.73.238]:64265 "EHLO host.almesberger.net") by vger.kernel.org with ESMTP id S261231AbUFVHuM (ORCPT ); Tue, 22 Jun 2004 03:50:12 -0400 To: Jens Axboe Content-Disposition: inline In-Reply-To: <20040622073919.GV12881@suse.de>; from axboe@suse.de on Tue, Jun 22, 2004 at 09:39:20AM +0200 List-Id: linux-fsdevel.vger.kernel.org Jens Axboe wrote: > I don't think a read-barrier currently has a meaning. A write barrier > will force ordering for later reads too, of course. That's one of the problem spots with priorities: if there are a lot of writes in the queue, high-priority reads will be delayed for a long time. But do we have cases where reads must not cross write barriers ? > It can't, the insert position doesn't tell you whether it's a barrier or > not. You have to check ->flags for that. Yet deadline, AS, and CFQ don't do any such check :-) - Werner -- _________________________________________________________________________ / Werner Almesberger, Buenos Aires, Argentina wa@almesberger.net / /_http://www.almesberger.net/____________________________________________/