They switched the default cache to writeback in qemu 1.2 which is shipped with F18. http://wiki.qemu.org/ChangeLog/1.2 F17 shipped with qemu version 1.0.1 which I think defaults to writethrough. If you don't change the command I'd think you should get writeback automatically after the upgrade. ----- Original Message ----- > From: Jonathan Masters <jcm@xxxxxxxxxx> > To: Jerry James <loganjerry@xxxxxxxxx> > Cc: Fedora ARM <arm@xxxxxxxxxxxxxxxxxxxxxxx> > Sent: Friday, January 11, 2013 2:12 PM > Subject: Re: Write-back vs. write-through for VMs > > Hi Jerry, > > I think you make a good recommendation, explaining the issue of write back via > cache vs. immediately hitting the disk. I also think your mail explains why we > should not change the default. Instead, lets change the documentation, to > explain that those not needing consistency can use this performance > optimization. > > Jon. > > -- > Sent from my iPad > > On Jan 11, 2013, at 10:42, Jerry James <loganjerry@xxxxxxxxx> wrote: > >> I've been using the vexpress image with QEMU to try to track down some >> ARM-specific problems in two of my packages. The VM was unbearably >> slow at first (by which I mean that a simple "yum upgrade" took > over 6 >> hours), until I changed: >> >> -sd "$IMAGE" >> >> to: >> >> -drive if=sd,cache=writeback,file="$IMAGE" >> >> in boot-vexpress and boot-vexpress+x. I'm well aware of the danger of >> using writeback, but ... it's a VM. With the script as shipped, my >> hard drive light was on constantly, and the entire host was slowed >> down dramatically due to insufficient disk bandwidth. With writeback >> on, I can re-create the VM and reinstall the packages of interest in >> very little time, certainly less than even simple operations were >> taking with write-through on. Is there some reason why changing the >> scripts to use writeback would not be a good idea? >> >> Regards, >> -- >> Jerry James >> http://www.jamezone.org/ >> _______________________________________________ >> arm mailing list >> arm@xxxxxxxxxxxxxxxxxxxxxxx >> https://admin.fedoraproject.org/mailman/listinfo/arm > _______________________________________________ > arm mailing list > arm@xxxxxxxxxxxxxxxxxxxxxxx > https://admin.fedoraproject.org/mailman/listinfo/arm > _______________________________________________ arm mailing list arm@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/arm
