.. _kernel-parameters: ACRN Kernel Parameters ###################### Generic kernel parameters ************************* A number of kernel parameters control the behavior of ACRN-based systems. Some are applicable to the Service VM kernel, others to the User VM kernel, and some are applicable to both. This section focuses on generic parameters from the Linux kernel which are relevant for configuring or debugging ACRN-based systems. .. list-table:: :header-rows: 1 :widths: 10,10,50,30 * - Parameter - Used in Service VM or User VM - Description - Usage example * - module_blacklist - Service VM - A comma-separated list of modules that should not be loaded. Useful to debug or work around issues related to specific modules. - :: module_blacklist=dwc3_pci * - no_timer_check - Service VM,User VM - Disables the code which tests for broken timer IRQ sources. - :: no_timer_check * - console - Service VM,User VM - Output console device and options. ``tty`` Use the virtual console device . ``ttyS[,options]`` Use the specified serial port and options. Default options are ``9600n8`` meaning 9600 baud, no parity, 8 bits. Options are of the form *bbbbpnf*, where: | *bbbb* is baud rate, for example 9600; | *p* is parity, one of ``n``, ``o``, or ``e`` (for none, odd, or even), | *n* is number of bits (typically 8), | *f* is flow control (``r`` for RTS, or left blank) ``hvc`` Use the hypervisor console device . (This is for both Xen and PowerPC hypervisors.) - :: console=tty0 console=ttyS0 console=hvc0 * - loglevel - Service VM - All Kernel messages with a loglevel less than the console loglevel will be printed to the console. The loglevel can also be changed with ``klogd`` or other programs. The loglevels are defined as follows: .. list-table:: :header-rows: 1 * - loglevel value - Definition * - 0 (KERN_EMERG) - system is unusable * - 1 (KERN_ALERT) - action must be taken immediately * - 2 (KERN_CRIT) - critical conditions * - 3 (KERN_ERR) - error conditions * - 4 (KERN_WARNING) - warning conditions * - 5 (KERN_NOTICE) - normal but significant condition * - 6 (KERN_INFO) - informational * - 7 (KERN_DEBUG) - debug-level messages - :: loglevel=7 * - ignore_loglevel - User VM - Ignoring loglevel setting will print **all** kernel messages to the console. Useful for debugging. We also add it as printk module parameter, so users could change it dynamically, usually by changing ``/sys/module/printk/parameters/ignore_loglevel``. - :: ignore_loglevel * - log_buf_len - User VM - Sets the size of the printk ring buffer, in bytes. n must be a power of two and greater than the minimal size. The minimal size is defined by LOG_BUF_SHIFT kernel config parameter. There is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter that allows to increase the default size depending on the number of CPUs. See init/Kconfig for more details." - :: log_buf_len=16M * - consoleblank - Service VM,User VM - The console blank (screen saver) timeout in seconds. Defaults to 600 (10 minutes). A value of 0 disables the blank timer. - :: consoleblank=0 * - rootwait - Service VM,User VM - Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices). - :: rootwait * - root - Service VM,User VM - Define the root filesystem ``/dev/`` represents the device number of the partition - device number of disk plus the partition number ``/dev/p`` same as above, this form is used when disk name of the partitioned disk ends with a digit. To separate disk name and partition slot, a 'p' is inserted. ``PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF`` representing the unique id of a partition if the partition table provides it. The UUID may be either an EFI/GPT UUID, or refer to an MSDOS partition using the format SSSSSSSS-PP, where SSSSSSSS is a zero-filled hexadecimal representation of the 32-bit "NT disk signature", and PP is a zero-filled hexadecimal representation of the 1-based partition number. - :: root=/dev/mmcblk0p1 root=/dev/vda2 root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF * - rw - Service VM,User VM - Mount root device read-write on boot - :: rw * - tsc - User VM - Disable clocksource stability checks for TSC. Format: , where the only supported value is: ``reliable``: Mark TSC clocksource as reliable, and disables clocksource verification at runtime, and the stability checks done at bootup. Used to enable high-resolution timer mode on older hardware, and in virtualized environments. - :: tsc=reliable * - cma - Service VM - Sets the size of the kernel global memory area for contiguous memory allocations, and optionally the placement constraint by the physical address range of memory allocations. A value of 0 disables CMA altogether. For more information, see ``include/linux/dma-contiguous``. - :: cma=64M@0 * - hvlog - Service VM - Reserve memory for the ACRN hypervisor log. The reserved space should not overlap any other blocks (e.g. hypervisor's reserved space). - :: hvlog=2M@0x6de00000 * - memmap - Service VM - Mark specific memory as reserved. ``memmap=nn[KMG]$ss[KMG]`` Region of memory to be reserved is from ``ss`` to ``ss+nn``, using ``K``, ``M``, and ``G`` representing Kilobytes, Megabytes, and Gigabytes, respectively. - :: memmap=0x400000$0x6da00000 * - ramoops.mem_address ramoops.mem_size ramoops.console_size - Service VM - Ramoops is an oops/panic logger that writes its logs to RAM before the system crashes. Ramoops uses a predefined memory area to store the dump. See `Linux Kernel Ramoops oops/panic logger `_ for details. - :: ramoops.mem_address=0x6da00000 ramoops.mem_size=0x400000 ramoops.console_size=0x200000 * - reboot_panic - Service VM - Reboot in case of panic The comma-delimited parameters are: reboot_mode: ``w`` (warm), ``s`` (soft), ``c`` (cold), or ``g`` (gpio) reboot_type: ``b`` (bios), ``a`` (acpi), ``k`` (kbd), ``t`` (triple), ``e`` (efi), or ``p`` (pci) reboot_cpu: ``s###`` (smp, and processor number to be used for rebooting) reboot_force: ``f`` (force), or not specified. - :: reboot_panic=p,w * - maxcpus - User VM - Maximum number of processors that an SMP kernel will bring up during bootup. ``maxcpus=n`` where n >= 0 limits the kernel to bring up ``n`` processors during system bootup. Giving n=0 is a special case, equivalent to ``nosmp``,which also disables the I/O APIC. After bootup, you can bring up additional plugged CPUs by executing ``echo 1 > /sys/devices/system/cpu/cpuX/online`` - :: maxcpus=1 * - nohpet - User VM - Don't use the HPET timer - :: nohpet * - intel_iommu - User VM - Intel IOMMU driver (DMAR) option ``on``: Enable intel iommu driver. ``off``: Disable intel iommu driver. ``igfx_off``: By default, gfx is mapped as normal device. If a gfx device has a dedicated DMAR unit, the DMAR unit is bypassed by not enabling DMAR with this option. In this case, gfx device will use physical address for DMA. - :: intel_iommu=off Intel GVT-g (AcrnGT) Parameters ******************************* This table gives an overview of all the Intel GVT-g parameters that are available to tweak the behavior of the graphics sharing (Intel GVT-g, aka AcrnGT) capabilities in ACRN. The `GVT-g-kernel-options`_ section below has more details on a few select parameters. .. list-table:: :header-rows: 1 :widths: 10,10,50,30 * - Parameter - Used in Service VM or User VM - Description - Usage example * - i915.enable_gvt - Service VM - Enable Intel GVT-g graphics virtualization support in the host - :: i915.enable_gvt=1 * - i915.enable_pvmmio - Service VM, User VM - Control Para-Virtualized MMIO (PVMMIO). It batches sequential MMIO writes into a shared buffer between the Service VM and User VM - :: i915.enable_pvmmio=0x1F * - i915.gvt_workload_priority - Service VM - Define the priority level of User VM graphics workloads - :: i915.gvt_workload_priority=1 * - i915.enable_initial_modeset - Service VM - On MRB, value must be ``1``. On NUC or UP2 boards, value must be ``0``. See :ref:`i915-enable-initial-modeset`. - :: i915.enable_initial_modeset=1 i915.enable_initial_modeset=0 * - i915.nuclear_pageflip - Service VM,User VM - Force enable atomic functionality on platforms that don't have full support yet. - :: i915.nuclear_pageflip=1 * - i915.avail_planes_per_pipe - Service VM - See :ref:`i915-avail-planes-owners`. - :: i915.avail_planes_per_pipe=0x01010F * - i915.domain_plane_owners - Service VM - See :ref:`i915-avail-planes-owners`. - :: i915.domain_plane_owners=0x011111110000 * - i915.domain_scaler_owner - Service VM - See `i915.domain_scaler_owner`_ - :: i915.domain_scaler_owner=0x021100 * - i915.enable_guc - Service VM - Enable GuC load for HuC load. - :: i915.enable_guc=0x02 * - i915.avail_planes_per_pipe - User VM - See :ref:`i915-avail-planes-owners`. - :: i915.avail_planes_per_pipe=0x070F00 * - i915.enable_guc - User VM - Disable GuC - :: i915.enable_guc=0 * - i915.enable_hangcheck - User VM - Disable check GPU activity for detecting hangs. - :: i915.enable_hangcheck=0 * - i915.enable_fbc - User VM - Enable frame buffer compression for power savings - :: i915.enable_fbc=1 .. _GVT-g-kernel-options: GVT-g (AcrnGT) Kernel Options details ===================================== This section provides additional information and details on the kernel command line options that are related to AcrnGT. i915.enable_gvt --------------- This option enables support for Intel GVT-g graphics virtualization support in the host. By default, it's not enabled, so we need to add ``i915.enable_gvt=1`` in the Service VM kernel command line. This is a Service OS only parameter, and cannot be enabled in the User VM. i915.enable_pvmmio ------------------ We introduce the feature named **Para-Virtualized MMIO** (PVMMIO) to improve graphics performance of the GVT-g guest. This feature batches sequential MMIO writes into a shared buffer between the Service VM and User VM, and then submits a para-virtualized command to notify to GVT-g in Service VM. This effectively reduces the trap numbers of MMIO operations and improves overall graphics performance. The ``i915.enable_pvmmio`` option controls the optimization levels of the PVMMIO feature: each bit represents a sub-feature of the optimization. By default, all sub-features of PVMMIO are enabled. They can also be selectively enabled or disabled.. The PVMMIO optimization levels are: * PVMMIO_ELSP_SUBMIT = 0x1 - Batch submission of the guest graphics workloads * PVMMIO_PLANE_UPDATE = 0x2 - Batch plane register update operations * PVMMIO_PLANE_WM_UPDATE = 0x4 - Batch watermark registers update operations * PVMMIO_MASTER_IRQ = 0x8 - Batch IRQ related registers * PVMMIO_PPGTT_UPDATE = 0x10 - Use PVMMIO method to update the PPGTT table of guest. .. note:: This parameter works in both the Service VM and User VM, but changes to one will affect the other. For example, if either Service VM or User VM disables the PVMMIO_PPGTT_UPDATE feature, this optimization will be disabled for both. i915.gvt_workload_priority -------------------------- AcrnGT supports **Prioritized Rendering** as described in the :ref:`GVT-g-prioritized-rendering` high-level design. This configuration option controls the priority level of GVT-g guests. Priority levels range from -1023 to 1023. The default priority is zero, the same priority as the Service VM. If the level is less than zero, the guest's priority will be lower than the Service VM, so graphics preemption will work and the prioritized rendering feature will be enabled. If the level is greater than zero, User VM graphics workloads will preempt most of the Service VM graphics workloads, except for display updating related workloads that use a default highest priority (1023). Currently, all User VMs share the same priority. This is a Service VM only parameters, and does not work in the User VM. .. _i915-enable-initial-modeset: i915.enable_initial_modeset --------------------------- At time, kernel graphics must be initialized with a valid display configuration with full display pipeline programming in place before the user space is initialized and without a fbdev & fb console. When ``i915.enable_initial_modeset=1``, the FBDEV of i915 will not be initialized, so users would not be able to see the fb console on screen. If there is no graphics UI running by default, users will see black screens displayed. When ``i915.enable_initial_modeset=0`` in Service VM, the plane restriction (also known as plane-based domain ownership) feature will be disabled. (See the next section and :ref:`plane_restriction` in the ACRN GVT-g High Level Design for more information about this feature.) In the current configuration, we will set ``i915.enable_initial_modeset=1`` in Service VM and ``i915.enable_initial_modeset=0`` in User VM. This parameter is not used on UEFI platforms. .. _i915-avail-planes-owners: i915.avail_planes_per_pipe and i915.domain_plane_owners ------------------------------------------------------- Both Service VM and User VM are provided a set of HW planes where they can display their contents. Since each domain provides its content, there is no need for any extra composition to be done through Service VM. ``i915.avail_planes_per_pipe`` and ``i915.domain_plane_owners`` work together to provide the plane restriction (or plan-based domain ownership) feature. * i915.domain_plane_owners On Intel's display hardware, each pipeline contains several planes, which are blended together by their Z-order and rendered to the display monitors. In AcrnGT, we can control each planes' ownership so that the domains can display contents on the planes they own. The ``i915.domain_plane_owners`` parameter controls the ownership of all the planes in the system, as shown in :numref:`i915-planes-pipes`. Each 4-bit nibble identifies the domain id owner for that plane and a group of 4 nibbles represents a pipe. This is a Service VM only configuration and cannot be modified at runtime. Domain ID 0x0 is for the Service VM, the User VM use domain IDs from 0x1 to 0xF. .. figure:: images/i915-image1.png :width: 900px :align: center :name: i915-planes-pipes i915.domain_plane_owners For example, if we set ``i915.domain_plane_owners=0x010001101110``, the plane ownership will be as shown in :numref:`i915-planes-example1` - Service VM (green) owns plane 1A, 1B, 4B, 1C, and 2C, and User VM #1 owns plane 2A, 3A, 4A, 2B, 3B and 3C. .. figure:: images/i915-image2.png :width: 900px :align: center :name: i915-planes-example1 i915.domain_plane_owners example Some other examples: * i915.domain_plane_owners=0x022211110000 - Service VM (0x0) owns planes on pipe A; User VM #1 (0x1) owns all planes on pipe B; and User VM #2 (0x2) owns all planes on pipe C (since, in the representation in :numref:`i915-planes-pipes` above, there are only 3 planes attached to pipe C). * i915.domain_plane_owners=0x000001110000 - Service VM owns all planes on pipe A and pipe C; User VM #1 owns plane 1, 2 and 3 on pipe B. Plane 4 on pipe B is owned by the Service VM so that if it wants to display notice message, it can display on top of the User VM. * i915.avail_planes_per_pipe Option ``i915.avail_planes_per_pipe`` is a bitmask (shown in :numref:`i915-avail-planes`) that tells the i915 driver which planes are available and can be exposed to the compositor. This is a parameter that must to be set in each domain. If ``i915.avail_planes_per_pipe=0``, the plane restriction feature is disabled. .. figure:: images/i915-image3.png :width: 600px :align: center :name: i915-avail-planes i915.avail_planes_per_pipe For example, if we set ``i915.avail_planes_per_pipe=0x030901`` in Service VM and ``i915.avail_planes_per_pipe=0x04060E`` in User VM, the planes will be as shown in :numref:`i915-avail-planes-example1` and :numref:`i915-avail-planes-example1`: .. figure:: images/i915-image4.png :width: 500px :align: center :name: i915-avail-planes-example1 Service VM i915.avail_planes_per_pipe .. figure:: images/i915-image5.png :width: 500px :align: center :name: i915-avail-planes-example2 User VM i915.avail_planes_per_pipe ``i915.avail_planes_per_pipe`` controls the view of planes from i915 drivers inside of every domain, and ``i915.domain_plane_owners`` is the global arbiter controlling which domain can present its content onto the real hardware. Generally, they are aligned. For example, we can set ``i915.domain_plane_owners= 0x011111110000``, ``i915.avail_planes_per_pipe=0x00000F`` in Service VM, and ``i915.avail_planes_per_pipe=0x070F00`` in domain 1, so every domain will only flip on the planes they owns. However, we don't force alignment: ``avail_planes_per_pipe`` might not be aligned with the setting of ``domain_plane_owners``. Consider this example: ``i915.domain_plane_owners=0x011111110000``, ``i915.avail_planes_per_pipe=0x01010F`` in Service VM and ``i915.avail_planes_per_pipe=0x070F00`` in domain 1. With this configuration, Service VM will be able to render on plane 1B and plane 1C, however, the content of plane 1B and plane 1C will not be flipped onto the real hardware. i915.domain_scaler_owner ======================== On each Intel GPU display pipeline, there are several plane scalers to zoom in/out the planes. For example, if a 720p video is played full-screen on a 1080p display monitor, the kernel driver will use a scaler to zoom in the video plane to a 1080p image and present it onto a display pipeline. (Refer to "Intel Open Source Graphics PRM Vol 7: display" for the details.) On Broxton platforms, Pipe A and Pipe B each have two plane scalers, and Pipe C has one plane scaler. To support the plane scaling in AcrnGT guest OS, we introduced the parameter ``i915.domain_scaler_owner``, to assign a specific scaler to the target guest OS. As with the parameter ``i915.domain_plane_owners``, each nibble of ``i915.domain_scaler_owner`` represents the domain id that owns the scaler; every nibble (4 bits) represents a scaler and every group of 2 nibbles represents a pipe. This is a Service VM only configuration and cannot be modified at runtime. Domain ID 0x0 is for the Service VM, the User VM use domain IDs from 0x1 to 0xF. For example, if we set ``i915.domain_scaler_owner=0x021100``, the Service VM owns scaler 1A, 2A; User VM #1 owns scaler 1B, 2B; and User VM #2 owns scaler 1C. i915.enable_hangcheck ===================== This parameter enable detection of a GPU hang. When enabled, the i915 will start a timer to check if the workload is completed in a specific time. If not, i915 will treat it as a GPU hang and trigger a GPU reset. In AcrnGT, the workload in Service VM and User VM can be set to different priorities. If Service VM is assigned a higher priority than the User VM, the User VM's workload might not be able to run on the HW on time. This may lead to the guest i915 triggering a hangcheck and lead to a guest GPU reset. This reset is unnecessary so we use ``i915.enable_hangcheck=0`` to disable this timeout check and prevent guest from triggering unnecessary GPU resets.