From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 00/10] PV-IO v3 Date: Mon, 20 Aug 2007 17:12:32 +0300 Message-ID: <46C9A150.60101@qumranet.com> References: <20070816231357.8044.55943.stgit@ghaskins-t60p.haskins.net><1187313953.6449.70.camel@localhost.localdomain><46C80C5B.7070009@qumranet.com> <1187617806.4363.179.camel@ghaskins-t60p.haskins.net> <64F9B87B6B770947A9F8391472E032160D4649E2@ehost011-8.exch011.intermedia.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, virtualization To: Dor Laor Return-path: In-Reply-To: <64F9B87B6B770947A9F8391472E032160D4649E2-yEcIvxbTEBqsx+V+t5oei8rau4O3wl8o3fe8/T/H7NteoWH0uzbU5w@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Dor Laor wrote: >>>> 2) We either need huge descriptors or some chaining >>>> >> mechanism to >> >>>> handle scatter-gather. >>>> >>>> >>> Or, my preference, have a small sglist in the descriptor; >>> >> Define "small" ;) >> >> There a certainly patterns that cannot/will-not take advantage of SG >> (for instance, your typical network rx path), and therefore the sg >> entries are wasted in some cases. Since they need to be (IMHO) u64, >> they suck down at least 8 bytes a piece. Because of this I elected to >> use the model of one pointer per descriptor, with an external >> > descriptor > >> for SG. What are your thoughts on this? >> > > Using Rusty's code there is no waste. > Each descriptor has a flag (head|next). Next flag stands for pointer to > the > next descriptor with u32 next index. So the waste is 4 bytes. > Sg descriptors are chained on the same descriptor ring. > Block I/O can easily require 256 sglist entries, eating up your ring. -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/