From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [VTD][patch 0/5] HVM device assignment using vt-d Date: Thu, 31 May 2007 16:52:25 +0100 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser , "Tian, Kevin" , Guy Zana , "Kay, Allen M" , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 31/5/07 16:40, "Keir Fraser" wrote: > It'd be interesting to know how these two approaches compare > performance-wise. I suppose yours should win, really, due to fewer physical > interrupts. One thing is that the polarity-switching approach is a slightly better fit with the HVM interrupt logic. Currently interrupt sources and VIOAPIC are not tightly bound together; they only interact by one waggling the virtual intx wires and the other sampling that wire periodically (or synchronously on +ve edges). Your approach requires a 'back channel' from the VIOAPIC code back to physical interrupt code to call ->end(). It's kind of ugly. On the other hand I suspect the polarity-switching code adds more stuff to the phsyical interrupt subsystem, and your approach can certainly be supported, probably by adding a bit more state (maybe just a single bit) per virtual intx wire. Really we need to look at and measure each implementation... -- Keir