Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 6 Feb 2001 12:39:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 6 Feb 2001 12:39:44 -0500 Received: from nat-pool.corp.redhat.com ([199.183.24.200]:36682 "EHLO devserv.devel.redhat.com") by vger.kernel.org with ESMTP id ; Tue, 6 Feb 2001 12:39:35 -0500 Date: Tue, 6 Feb 2001 12:37:26 -0500 (EST) From: Ben LaHaise To: "Stephen C. Tweedie" cc: Linus Torvalds , Alan Cox , Manfred Spraul , Steve Lord , , , Ingo Molnar Subject: Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait In-Reply-To: <20010206170506.H1167@redhat.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Hey folks, On Tue, 6 Feb 2001, Stephen C. Tweedie wrote: > The whole point of the post was that it is merging, not splitting, > which is troublesome. How are you going to merge requests without > having chains of scatter-gather entities each with their own > completion callbacks? Let me just emphasize what Stephen is pointing out: if requests are properly merged at higher layers, then merging is neither required nor desired. Traditionally, ext2 has not done merging because the underlying system doesn't support it. This leads to rather convoluted code for readahead which doesn't result in appropriately merged requests on indirect block boundries, and in fact leads to suboptimal performance. The only case I see where merging of requests can improve things is when dealing with lots of small files. But we already know that small files need to be treated differently (fe tail merging). Besides, most of the benefit of merging can be had by doing readaround for these small files. As for io completion, can't we just issue seperate requests for the critical data and the readahead? That way for SCSI disks, the important io should be finished while the readahead can continue. Thoughts? -ben - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/