Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261352AbVDDTlc (ORCPT ); Mon, 4 Apr 2005 15:41:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261357AbVDDTlc (ORCPT ); Mon, 4 Apr 2005 15:41:32 -0400 Received: from ida.rowland.org ([192.131.102.52]:4868 "HELO ida.rowland.org") by vger.kernel.org with SMTP id S261352AbVDDTkb (ORCPT ); Mon, 4 Apr 2005 15:40:31 -0400 Date: Mon, 4 Apr 2005 15:40:27 -0400 (EDT) From: Alan Stern X-X-Sender: stern@ida.rowland.org To: kus Kusche Klaus cc: Ingo Molnar , , Subject: RE: 2.6.11, USB: High latency? In-Reply-To: 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 Content-Length: 1428 Lines: 34 On Mon, 4 Apr 2005, kus Kusche Klaus wrote: > I asked our hardware team. The hardware has two devices which are > in use and capable of busmaster/DMA transfers: > The intel e100 ethernet controller and the intel PIIX4 USB > controller. > The IDE interface is also a busmaster, but there are only PIO IDE > devices. > > I suspect the latter, as USB reads were running in parallel... > How many bytes are transferred at most by the USB controller > for a single request? How long may this take? Your questions aren't very clear. The USB controller will do intermittent DMA (once per millisecond) even when no USB transfers are pending, so long as a USB device is attached. When transfers are pending it will do as much DMA as required to complete the transfers. The amount of time depends on the amount of data to be transferred and the speed at which the device can provide/accept the data. For Bulk transfers the DMA activity is more or less continual. > Any experiences / opinitions / advices? I've had plenty of experience using USB, but none in measuring bus utilization. However my guess is that the controller puts a fairly large load on the system. Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/