Resizable BAR

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Revision as of 11:01, 18 July 2025 by Admin (talk | contribs) (Created page with "== Resizable BAR == Resizable BAR is an optional PCI Express interface technology that allows the graphics card to access a larger portion of system memory, potentially improving performance in some games and applications. Resizable BAR is only useful to increase the buffer size for device to device memory copies, as in CPU memory to (dedicated) GPU memory. It is a way to enhance bandwidth and latency over PCIe links. The BAR is basically a channel between the GPU comm...")
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Resizable BAR

Resizable BAR is an optional PCI Express interface technology that allows the graphics card to access a larger portion of system memory, potentially improving performance in some games and applications.


Resizable BAR is only useful to increase the buffer size for device to device memory copies, as in CPU memory to (dedicated) GPU memory. It is a way to enhance bandwidth and latency over PCIe links. The BAR is basically a channel between the GPU command and memory areas and the CPU address space. so that, The Resizable BAR is an extension that just allows that address space to be changed "on the fly" so that the CPU can essentially blast data into a larger address space on the GPU. [1]


This blog explains how to update NVIDIA Resizable BAR firmware update on GeForce RTX 30 Series. you will find links to the most common OEM partners and their respective flash utilities at this site[2]

#If this GPU would [[support]] Resizable BAR the Total memory would be the whole VRAM size of the card, 
# for example, RTX 3060TI GPU is 8192  MiB. That means I need to update the GPU VBIOS.
$ nvidia-smi -q | grep -i bar -A 3               │
    BAR1 Memory Usage                                                                        │
        Total                             : 8192 MiB                                        │
        Used                              : 13 MiB                                            │
        Free                              : 8179 MiB

To enable Resizable BAR

Check for Resizable BAR Support:

Use lspci -v to identify your graphics card and see if it shows a "Supports Resizeable BAR" flag.


Using BIOS

  1. Enter the system’s BIOS/UEFI firmware configuration menu by pressing the DEL key during system start up. This key may vary between each system manufacturer, please check with your system manufacturer for specific instructions as necessary.
  2. Compatibility Support Module (CSM) or Legacy Mode must be disabled and UEFI boot mode must be Enabled.
  3. Ensure the following settings are set to Enabled (or Auto if the Enabled option is not present):
    1. Above 4G Decoding
    2. Re-Size BAR Support


Using Kernel param[3]

  1. Add nvidia.NVreg_EnableResizableBar=1 option for NVIDIA[4] to the GRUB_CMDLINE_LINUX_DEFAULT line of /etc/default/grub file
  2. Rebooting the system

References

  1. ↑ https://superuser.com/questions/1822675/does-resizable-bar-for-the-gpu-apply-to-shared-memory-chipsets
  2. ↑ https://nvidia.custhelp.com/app/answers/detail/a_id/5165
  3. ↑ https://www.kernel.org/doc/html/v4.16/admin-guide/kernel-parameters.html
  4. ↑ https://github.com/NVIDIA/open-gpu-kernel-modules/blob/main/kernel-open/nvidia/nv-pci.c#L170
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