stillrace.blogg.se - Qemu vga settings

Qemu vga settings drivers#
Qemu vga settings full#

3.7.4 Connecting VLANs between QEMU instances.3.7.3 Using the user mode network stack.3.6.1 Quick start for disk image creation.

Qemu vga settings full#

Default vram value, 16 MB, is fine for most common uses, except for full HD on Wayland (needs twice as much due to two framebuffers-page-flipping).

Multihead is not supported on any of the drivers.

The better choice of the two is clearly vnc/vga.

As the result, physical RAM may be wasted for no useful purpose.

Excel or Firefox) for purposes not necessarily very important for graphics performance.

Qemu vga settings drivers#

The extra (above required minimum) memory may be actually utilized by the guest OS drivers and applications (e.g. It may not be a good idea to use excessively large memory values just to be safe. But developers strongly recommend using at least vgamem * 2.

Note: An alternative formula for vram is screen_width * screen_height * 4 * (number_of_heads + 1).

Note: ram may (or may not) work with much smaller values, but it’s suggested to set it at least so that ram + vram >= 3 * vgamem.

Note: ram may (or may not) work even when it’s reduced to 2 * vgamem, but developers recommend using the larger value.

vgamem = screen_width * screen_height * 4 * number_of_heads.

vgamem = screen_width * screen_height * 4.

The recommended memory sizes are dependent on particular guest OS and its drivers: Video RAM is allocated in addition to specified guest main RAM, not within it. This is not a strict requirement, it’s just advised. TODO: Check what happens when we specify more.Īll memory sizes should be specified as powers of 2. We don’t assume such setups when computing memory values.ĭue to 32-bit addressing in QEMU, total (for all video cards together) maximum size of ram is 256 or 512 MB. But if three screens are in a row and the fourth screen is below them then the required memory may correspond (depending on the driver) to 4.5 (3072x1536) megapixels when all the screens are arranged diagonally, it’s 12 (4096x3072) megapixels. If they are arranged compactly in a single row or in two rows and two columns, it’s fine, memory for 3 megapixels is required. For instance, let’s assume 4 screens with resolution 1024x768 each. But this should actually be the bounding rectangle of the screen arrangement. The required memory sizes are basically dependent on screen resolution multiplied by number of heads. Maximum supported screen resolution is 4 megapixels (2560x1600). Minimum ram size, as enforced by QEMU regardless the command line settings, is 2 * vgamem. libvirt vram represents secondary memory bar, 64-bit (it may not be true as of now, there is a separate vram_size_mb QEMU command line option for that, not necessarily used by libvirt).

Libvirt ram represents primary memory bar, 32-bit only. But don’t rely on anything, things may change, so it’s a good idea to get confirmation from QEMU and/or libvirt developers about everything. You can look for implementation details in qxl.c in QEMU sources. This can be done using before_vm_start VDSM hook. Users should be able to override the computed default settings if they use uncommon arrangements or the computed values don’t work well for them. Nobody knows the perfect ultimate answer to that topic, there are different guest OS drivers and as stated above, things may completely change in oVirt 4. Please note that all the information about video RAM sizes below should be taken with grain of salt. vgamem libvirt option is available since RHEL-7.1 vgamem_mb QEMU option is available since RHEL-6.7. vgamem (KB) must be set to at least certain minimum value based on screen resolution and number of heads, corresponds to vgamem_mb (MB) QEMU command line option.vram (KB) specifies secondary memory bar size, corresponds to vram_size (B) QEMU command line option.ram (KB) specifies primary memory bar size, corresponds to ram_size (B) QEMU command line option.Meanings of element attributes in domain XML: If single-PCI option is set, there is only single video device and “heads” Engine option transforms to number_of_heads above. Note: If single-PCI option is not set, number_of_heads is always 1 and “heads” option in the Engine defines number of separate video devices. vgamem = unset (default 16 MB set by libvirt).The following video RAM settings were applied in oVirt per PCI device: This page provides compilation of information on the topic gathered from many sources and represents the best knowledge available as of December 2015. There is a lot of confusion about video RAM settings and workings in libvirt/QEMU. It is not user documentation and should not be treated as such.ĭocumentation is available here. This developer documentation is outdated, but provides historical context.