Re: [Qemu-devel] [PATCH] [RFC] Variable video ram size option

[Trolle Selander <trolle.selander@eu.citrix.com>]

Avi Kivity wrote:
> Trolle Selander wrote:
>> These patches are "extracted" from a patch-set I made for Xen. Any 
>> xen-specific parts have been removed. The patches do away with the 
>> statically defined VGA_RAM_ SIZE and provides a new -videoram option 
>> to enable setting the amount of video ram available to the VM. 
>> Shrinking default video ram used to 4 Megs (which is all that the 
>> default Cirrus card can use, anyway - previously, there's been a 
>> "waste" of 4 megs with the statically defined 8 Megs), but allowing 
>> users to specify up to 16 Megs of vram, to support the very high 
>> resolutions such as 2560x1600x32 that are available on today's 
>> high-end displays.
>> The vgabios patch is needed for this to work, both for the variable 
>> size video ram, and to add the new resolutions. The defines for the 
>> high resolution and wide-screen modes were taken from what is already 
>> in qemu-kvm, so getting this into qemu mainline should get qemu/kvm & 
>> xen "in sync" in this regard.
>>
>> Special thanks to Stefano Stabellini for comments & constructive 
>> criticism, and some save/restore fixes on the Xen version of this 
>> patch-set.
>>
>> I'll brace myself for reports of how this patch breaks all the 
>> non-x86 architectures that qemu emulates... :)
>> @@ -178,7 +178,7 @@
>>     to store the VM snapshots */
>>  DriveInfo drives_table[MAX_DRIVES+1];
>>  int nb_drives;
>> -static int vga_ram_size;
>> +static int vga_ram_size = 4 * 1024 * 1024;
>>  enum vga_retrace_method vga_retrace_method = VGA_RETRACE_DUMB;
>>  DisplayState display_state;
>>  int nographic;
>
> You're changing the default, which will break existing setups.
>
My bad. That was actually a small xen "leftover", where the previous 
default for stdvga didn't matter, since  VBE had never been enabled and 
the 8 megs allocated for it by default had never actually been used, so 
it was "safe" to break the default there. The probably shouldn't be a 
"global" default now anyway, but a separate default per emulated card - 
current 4 for Cirrus, and 8 for stdvga & vmware. I suppose it would be 
possible to also add the ability to set cirrus down to 2 megs for cirrus 
too - pretty much everything is already in the code to emulate the 2 meg 
model anyway.
All things considered, I consider it rather encouraging that no one has 
found anything other than memory defaults & limits to remark on so far. :)

-- Trolle