# Configuring Kernel Boot Parameters

Kernel boot parameters are command-line arguments passed to the Linux kernel at boot time to configure the settings and behaviors of the system. You can use these parameters to control and optimize the behavior of the GPU driver.

## Enabling long-running compute workloads

The Intel graphics kernel driver defaults to preventing compute workloads from running longer than four seconds to avoid errant shaders from blocking desktop operations. You can modify this setting via the i915 kernel module parameter `enable_hangcheck`. Follow these steps to check and modify the default setting.

1. Check your current setting.

   ```bash
   sudo cat /sys/module/i915/parameters/enable_hangcheck
   ```

   A default value of Y indicates that the hang check is currently active.

2. Change the current setting at runtime.

   ```bash
   echo N | sudo tee /sys/module/i915/parameters/enable_hangcheck
   ```

3. To persist the value after reboot, change the default setting by
passing `i915.enable_hangcheck=0`​ in your `GRUB_CMDLINE_LINUX_DEFAULT`
setting. You can add the option using instructions provided by your operating
system provider or by editing the value of `GRUB_CMDLINE_LINUX_DEFAULT` in
`/etc/default/grub` to include `i915.enable_hangcheck=0`.

   After editing, the line for `GRUB_CMDLINE_LINUX_DEFAULT` should look similar
   to the following:
   
   ```bash
   GRUB_CMDLINE_LINUX_DEFAULT="i915.enable_hangcheck=0"
   ```

4. Update the GRUB boot files:

   ::::{tab-set}
   
   :::{tab-item} RHEL and SUSE
   ```bash
   grub2-mkconfig -o /boot/grub2/grub.cfg
   ```
   :::
   
   :::{tab-item} Ubuntu
   ```bash
   update-grub
   ```
   :::
   
   ::::

5. Reboot your system.

   ```bash
   sudo reboot
   ```

6. Confirm that `i915.enable_hangcheck=0` is present in the kernel boot parameters.

   ```bash
   cat /proc/cmdline
   ```

   Ensure that the output includes `i915.enable_hangcheck=0`.

7. Check the current value of the `enable_hangcheck` parameter for the i915 module to ensure it is set to 0.

   ```bash
   cat /sys/module/i915/parameters/enable_hangcheck
   ```

## Disabling PCI reallocation

Some systems may have compatibility issues between the system BIOS and the Linux kernel Memory-Mapped I/O Base Address Register (MMIO BAR) reallocation, which prevents the Intel® Data Center GPUs from being accessible after the system boots. If you encounter problems with multi-card solutions where the Intel GPU devices fail to initialize, for example, entries for the device are not enumerating in `/dev/dri`, you can work around the issue by disabling PCI reallocation. The following instruction explains how to do that.

1. Check current boot parameters to determine if your system already has `pci=realloc=off` set.

   ```bash
   cat /proc/cmdline
   ```
   Look for the presence of `pci=realloc=off` in the output.

2. If `pci=realloc=off` is not present, open the GRUB configuration file in a text editor.

   ```bash
   sudo nano /etc/default/grub
   ```

3. Find the line that starts with `GRUB_CMDLINE_LINUX_DEFAULT` and modify it to include `pci=realloc=off`. The line should look similar to the following example.

   ```bash
   GRUB_CMDLINE_LINUX_DEFAULT="pci=realloc=off"
   ```

4. Update the GRUB boot files to apply the changes.

   ::::{tab-set}
   
   :::{tab-item} RHEL and SUSE
   ```bash
   grub2-mkconfig -o /boot/grub2/grub.cfg
   ```
   :::
   
   :::{tab-item} Ubuntu
   ```bash
   update-grub
   ```
   :::
   
   ::::

5. Reboot your system.

   ```bash
   sudo reboot
   ```

6. Verify that `pci=realloc=off` is now present in the boot parameters.

   ```bash
   cat /proc/cmdline
   ```