On Tue, Aug 03, 2010 at 04:19:39PM +0300, Avi Kivity wrote: > On 08/03/2010 03:48 PM, Richard W.M. Jones wrote: > > > >Thanks for the explanation. I'll repost my "DMA"-like fw-cfg patch > >once I've rebased it and done some more testing. This huge regression > >for a common operation (implementing -initrd) needs to be solved > >without using inb/rep ins. > > Adding more interfaces is easy but a problem in the long term. > We'll optimize it as much as we can. Meanwhile, why are you loading > huge initrds? Use a cdrom instead (it will also be faster since the > guest doesn't need to unpack it). Because it involves rewriting the entire appliance building process, and we don't necessarily know if it'll be faster after we've done that. Look: currently we create the initrd on the fly in 700ms. We've no reason to believe that creating a CD-ROM on the fly wouldn't take around the same time. After all, both processes involve reading all the host files from disk and writing a temporary file. You have to create these things on the fly, because we don't actually ship an appliance to end users, just a tiny (< 1 MB) skeleton. You can't ship a massive statically linked appliance to end users because it's just unmanageable (think: security; updates; bandwidth). Loading the initrd currently takes 115ms (or could do, if a sensible 50 line patch was permitted). So the only possible saving would be the 115ms load time of the initrd. In theory the CD-ROM device could be detected in 0 time. Total saving: 115ms. But will it be any faster, since after spending 115ms, everything runs from memory, versus being loaded from the CD? Let's face the fact that qemu has suffered from an enormous regression. From some hundreds of milliseconds up to over a minute, in the space of 6 months of development. For a very simple operation: loading a file into memory. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://et.redhat.com/~rjones/virt-top -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
