Hi Mark, On 17.8.2014 18:16, Mark Cave-Ayland wrote: > Another issue I've found with my OpenBIOS tests is that HelenOS PPC > appears to be quite sluggish under the latest qemu-system-ppc. I've > attempted a few bisections but it's quite tricky to tie the regression > down to one particular commit. > > The slowness starts to appear in a minor form with the 1.6 timer rewrite > and seems to have become worse with newer QEMU releases. There have been > various changes to the OpenBIOS frequency/tb-frequency properties in > order to support OS X PPC in this timeframe so I'm wondering if somehow > HelenOS is exposing a bug in the qemu-system-ppc timer emulation? > > In order to reproduce, grab a QEMU 2.1 release tarball, compile and > install and then launch like this: > > qemu-system-ppc -cdrom HelenOS-0.5.0-ppc32.iso -m 512 -boot d > > As soon as the main kernel executes you can see the delay in writing > characters to the VGA console.
I also noticed that as of QEMU 2.0, HelenOS/ppc32 under QEMU became quite slow. Now, I am not a ppc32 expert either, but I suspect that the problem is related to the way HelenOS programs the decrementer exception. It always does so using the instruction below: mtdec reg ; reg = 1000 So we always use constant 1000, regardless of what the real frequency property is. I guess this is a constant which used to work reasonably well under PearPC back then and has stayed ever since. *Martin*, correct me if I am wrong, please. Btw, was the actual frequency increased? That could explain why HelenOS/ppc32 became slower - with more exceptions you'd have bigger overhead. Jakub _______________________________________________ HelenOS-devel mailing list [email protected] http://lists.modry.cz/listinfo/helenos-devel
