From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gordan Bobic Subject: Re: =?utf-8?q?USB_passthrough_burning_5=25_of_CPU=3F?= Date: Mon, 05 Aug 2013 15:01:45 +0100 Message-ID: References: <446278be57f7b83e771e9306f7172d96@mail.shatteredsilicon.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap Cc: Felipe Franciosi , xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Mon, 5 Aug 2013 14:57:09 +0100, George Dunlap wrote: > On Mon, Aug 5, 2013 at 1:28 PM, Gordan Bobic > wrote: >> Ever since I switched from passing a PCI USB controller >> through to a domU in favour of passing USB devices using >> the "usbdevice" config parameter, the domU affected >> seems to have qemu-dm "idling" at about 5% CPU usage in >> dom0. With the PCI USB controller passed through, this >> does not happen. >> >> Is this normal/expected? Does a similar continuous CPU >> overhead invisibly apply to PCI passthrough devices as >> well? Or is this CPU tax only applicable to USB >> passthrough? > > Do you have the emulated USB controller enabled when you're passing > through the PCI USB controller? Yes, but nothing is hanging off it (well, other than maybe the emulated VNC mouse/keyboard). > My understanding was that certain USB devices must, by specification, > be polled something like a hundred times per second. QEMU has to > emulate every one of these. One of the things XenServer does for > really high-density VDI deployments, I believe, is disable USB in the > guests entirely. So it stands to reason that with no physical USB devices passed through the USB controller polling gets optimized out. Gordan