From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=55210 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OgeW4-0001PV-VV for qemu-devel@nongnu.org; Wed, 04 Aug 2010 10:00:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OgeW3-0003Wj-JE for qemu-devel@nongnu.org; Wed, 04 Aug 2010 10:00:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:10025) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OgeW3-0003WU-5r for qemu-devel@nongnu.org; Wed, 04 Aug 2010 10:00:19 -0400 Date: Wed, 4 Aug 2010 17:00:11 +0300 From: Gleb Natapov Subject: Re: [Qemu-devel] Anyone seeing huge slowdown launching qemu with Linux 2.6.35? Message-ID: <20100804140011.GR10499@redhat.com> References: <4C586CF9.7030206@redhat.com> <4C588804.5060803@redhat.com> <4C590046.2020705@redhat.com> <4C591D48.9080301@redhat.com> <4C592218.3000901@redhat.com> <4C596549.1070109@codemonkey.ws> <20100804130709.GL10499@redhat.com> <4C5967D8.7080707@codemonkey.ws> <20100804133401.GP10499@redhat.com> <4C5970AC.6060105@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4C5970AC.6060105@codemonkey.ws> List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: qemu-devel@nongnu.org, "Richard W.M. Jones" , Avi Kivity , kvm@vger.kernel.org, Gerd Hoffmann On Wed, Aug 04, 2010 at 08:52:44AM -0500, Anthony Liguori wrote: > On 08/04/2010 08:34 AM, Gleb Natapov wrote: > >On Wed, Aug 04, 2010 at 08:15:04AM -0500, Anthony Liguori wrote: > >>On 08/04/2010 08:07 AM, Gleb Natapov wrote: > >>>On Wed, Aug 04, 2010 at 08:04:09AM -0500, Anthony Liguori wrote: > >>>>On 08/04/2010 03:17 AM, Avi Kivity wrote: > >>>>>For playing games, there are three options: > >>>>>- existing fwcfg > >>>>>- fwcfg+dma > >>>>>- put roms in 4GB-2MB (or whatever we decide the flash size is) > >>>>>and have the BIOS copy them > >>>>> > >>>>>Existing fwcfg is the least amount of work and probably > >>>>>satisfactory for isapc. fwcfg+dma is IMO going off a tangent. > >>>>>High memory flash is the most hardware-like solution, pretty easy > >>>>>from a qemu point of view but requires more work. > >>>> > >>>>The only trouble I see is that high memory isn't always available. > >>>>If it's a 32-bit PC and you've exhausted RAM space, then you're only > >>>>left with the PCI hole and it's not clear to me if you can really > >>>>pull out 100mb of space there as an option ROM without breaking > >>>>something. > >>>> > >>>We can map it on demand. Guest tells qemu to map rom "A" to address X by > >>>writing into some io port. Guest copies rom. Guest tells qemu to unmap > >>>it. Better then DMA interface IMHO. > >>That's what I thought too, but in a 32-bit guest using ~3.5GB of > >>RAM, where can you safely get 100MB of memory to full map the ROM? > >>If you're going to map chunks at a time, you are basically doing > >>DMA. > >> > >This is not like DMA event if done in chunks and chunks can be pretty > >big. The code that dials with copying may temporary unmap some pci > >devices to have more space there. > > That's a bit complicated because SeaBIOS is managing the PCI devices > whereas the kernel code is running as an option rom. I don't know > the BIOS PCI interfaces well so I don't know how doable this is. > Unmapping device and mapping it at the same place is easy. Enumerating pci devices from multiboot.bin looks like unneeded churn though. > Maybe we're just being too fancy here. > > We could rewrite -kernel/-append/-initrd to just generate a floppy > image in RAM, and just boot from floppy. > May be. Can floppy be 100M? -- Gleb.