On Tue, May 07, 2013 at 07:01:13PM -0400, Kevin O'Connor wrote:
On Tue, May 07, 2013 at 09:00:48PM +0300, Michael S. Tsirkin wrote:
On Thu, Apr 25, 2013 at 12:02:20PM +0300, Michael S. Tsirkin wrote:
Untested yet, but I thought I'd share the BIOS bits so we can agree on direction.
In particular check out ROM sizes:
- Before patchset with DSDT enabled Total size: 127880 Fixed: 59060 Free: 3192 (used 97.6% of 128KiB rom)
- Before patchset with DSDT disabled Total size: 122844 Fixed: 58884 Free: 8228 (used 93.7% of 128KiB rom)
- After patchset: Total size: 128776 Fixed: 59100 Free: 2296 (used 98.2% of 128KiB rom)
- Legacy disabled at build time: Total size: 119836 Fixed: 58996 Free: 11236 (used 91.4% of 128KiB rom)
As can be seen from this, most size savings come from dropping DSDT, but we do save a bit by removing other tables. Of course the real reason to move tables to QEMU is so that ACPI can better match hardware.
This patchset adds an option to move all code for formatting acpi tables out of BIOS. With this, QEMU has full control over the table layout. All tables are loaded from the new "/etc/acpi/" directory. Any entries in this directory cause BIOS to disable ACPI table generation completely. A generic linker script, controlled by QEMU, is loaded from "/etc/linker-script". It is used to patch in table pointers and checksums.
After some thought, there are two additional options worth considering, in that they simplify bios code somewhat:
bios could get size from qemu, allocate a buffer (e.g. could be one buffer for all tables) and pass the address to qemu. qemu does all the patching
further, qemu could do the copy of tables into that address directly
This seems more complex than necessary to me.
The important task is to get the tables generated in QEMU - I'd focus on getting the tables generated in QEMU (one table per fw_cfg "file"). Once that is done, the SeaBIOS side can be easily implemented, and we can add any enhancements on top if we feel it is necessary.
-Kevin
I have kind of done this, though only compile-tested for now - still need to update the bios with the new linker interface along the lines suggested by you.
If you want to see how the code looks like check out
git://git.kernel.org/pub/scm/virt/kvm/mst/qemu.git acpi the code is in hw/i386/acpi-build.c and hw/i386/bios-linker-loader.c
the history is all messed up now, I'll clean it up shortly.
That said, this uses fw_cfg so for this to be acceptable, we need to fix migration with big fw_cfg files.