Hi Alex, Follow some comments and questions.
On 05/02, Alex Deucher wrote: > Add an initial documentation page for user mode queues. > > Signed-off-by: Alex Deucher <alexander.deuc...@amd.com> > --- > Documentation/gpu/amdgpu/index.rst | 1 + > Documentation/gpu/amdgpu/userq.rst | 196 +++++++++++++++++++++++++++++ > 2 files changed, 197 insertions(+) > create mode 100644 Documentation/gpu/amdgpu/userq.rst > > diff --git a/Documentation/gpu/amdgpu/index.rst > b/Documentation/gpu/amdgpu/index.rst > index bb2894b5edaf2..45523e9860fc5 100644 > --- a/Documentation/gpu/amdgpu/index.rst > +++ b/Documentation/gpu/amdgpu/index.rst > @@ -12,6 +12,7 @@ Next (GCN), Radeon DNA (RDNA), and Compute DNA (CDNA) > architectures. > module-parameters > gc/index > display/index > + userq > flashing > xgmi > ras > diff --git a/Documentation/gpu/amdgpu/userq.rst > b/Documentation/gpu/amdgpu/userq.rst > new file mode 100644 > index 0000000000000..53e6b053f652f > --- /dev/null > +++ b/Documentation/gpu/amdgpu/userq.rst > @@ -0,0 +1,196 @@ > +================== > + User Mode Queues > +================== > + > +Introduction > +============ > + > +Similar to the KFD, GPU engine queues move into userspace. The idea is to > let > +user processes manage their submissions to the GPU engines directly, > bypassing > +IOCTL calls to the driver to submit work. This reduces overhead and also > allows > +the GPU to submit work to itself. Applications can set up work graphs of > jobs > +across multiple GPU engines without needing trips through the CPU. > + > +UMDs directly interface with firmware via per application shared memory > areas. > +The main vehicle for this is queue. A queue is a ring buffer with a read > +pointer (rptr) and a write pointer (wptr). The UMD writes IP specific > packets > +into the queue and the firmware processes those packets, kicking off work on > the > +GPU engines. The CPU in the application (or another queue or device) updates > +the wptr to tell the firmware how far into the ring buffer to process packets > +and the rtpr provides feedback to the UMD on how far the firmware has > progressed > +in executing those packets. When the wptr and the rptr are equal, the queue > is > +idle. > + > +Theory of Operation > +=================== > + > +The various engines on modern AMD GPUs support multiple queues per engine > with a > +scheduling firmware which handles dynamically scheduling user queues on the > +available hardware queue slots. When the number of user queues outnumbers > the > +available hardware queue slots, the scheduling firmware dynamically maps and > +unmaps queues based on priority and time quanta. The state of each user > queue > +is managed in the kernel driver in an MQD (Memory Queue Descriptor). This > is a > +buffer in GPU accessible memory that stores the state of a user queue. The > +scheduling firmware uses the MQD to load the queue state into an HQD > (Hardware > +Queue Descriptor) when a user queue is mapped. Each user queue requires a > +number of additional buffers which represent the ring buffer and any metadata > +needed by the engine for runtime operation. On most engines this consists of > +the ring buffer itself, a rptr buffer (where the firmware will shadow the > rptr > +to userspace), a wrptr buffer (where the application will write the wptr for > the > +firmware to fetch it), and a doorbell. A doorbell is a piece of the device's In this part, you started to explain about the doorbell; consider adding a new paragraph here. Another idea could be to create a dedicated page to explain doorbells and move all the general doorbell information from this patch to the new page. I think there is no kernel-doc about amdgpu doorbells. > +MMIO BAR which can be mapped to specific user queues. Writing to the > doorbell > +wakes the firmware and causes it to fetch the wptr and start processing the > +packets in the queue. Each 4K page of the doorbell BAR supports specific > offset > +ranges for specific engines. The doorbell of a queue most be mapped into the /most/must/ > +aperture aligned to the IP used by the queue (e.g., GFX, VCN, SDMA, etc.). > +These doorbell apertures are set up via NBIO registers. Doorbells are 32 > bit or > +64 bit (depending on the engine) chunks of the doorbell BAR. A 4K doorbell > page > +provides 512 64-bit doorbells for up to 512 user queues. A subset of each > page > +is reserved for each IP type supported on the device. The user can query the > +doorbell ranges for each IP via the INFO IOCTL. The first time that I read this, I was confused about the IOCTL part; however, at the end of this patch, I noticed that you explained the IOCTL part. Perhaps add a mention in parenthesis so the reader can see more details about this info in the "IOCTL Interfaces" section. > + > +When an application wants to create a user queue, it allocates the the > necessary > +buffers for the queue (ring buffer, wptr and rptr, context save areas, etc.). > +These can be separate buffers or all part of one larger buffer. The > application > +would map the buffer(s) into its GPUVM and use the GPU virtual addresses of > for > +the areas of memory they want t use for the user queue. They would also /t/to/ > +allocate a doorbell page for the doorbells used by the user queues. The > +application would then populate the MQD in the USERQ IOCTL structure with the > +GPU virtual addresses and doorbell index they want to use. The user can also > +specify the attributes for the user queue (priority, whether the queue is > secure > +for protected content, etc.). The application would then call the USERQ > +create IOCTL to create the queue from using the specified MQD. The > +kernel driver then validates the MQD provided by the application and > translates > +the MQD into the engine specific MQD format for the IP. The IP specific MQD > +would be allocated and the queue would be added to the run list maintained by > +the scheduling firmware. Once the queue has been created, the application > can > +write packets directly into the queue, update the wptr, and write to the > +doorbell offset to kick off work in the user queue. > + > +When the application is done with the user queue, it would call the USERQ > +FREE IOCTL to destroy it. The kernel driver would preempt the queue and > +remove it from the scheduling firmware's run list. Then the IP specific MQD > +would be freed and the user queue state would be cleaned up. Is it possible to add some pseudo-code that summarizes the programming model described here? > + > +Some engines may require the aggregated doorbell to if the engine does not /to/too/ or /to//? Do you know which engines requires the aggreted doorbell? Can this information be retrieved via IOCTL? I think this information can be helpful for userspace implementation. > +support doorbells from unmapped queues. The aggregated doorbell is a special > +page of doorbell space which wakes the scheduler. In cases where the engine > may > +be oversubscribed, some queues may not be mapped. If the doorbell is rung > when > +the queue is not mapped, the engine firmware may miss the request. Some > +scheduling firmware may work around this my polling wptr shadows when the > +hardware is oversubscribed, other engines may support doorbell updates from > +unmapped queues. In the event that one of these options is not available, > the > +kernel driver will map a page of aggregated doorbell space into each GPUVM > +space. The UMD will then update the doorbell and wptr as normal and then > write > +to the aggregated doorbell as well. > + > +Special Packets > +--------------- > + > +In order to support legacy implicit synchronization, as well as mixed user > and > +kernel queues, we need a synchronization mechanism that is secure. Because > +kernel queues or memory management tasks depend on kernel fences, we need a > way > +for user queues to update memory that the kernel can use for a fence, that > can't > +be messed with by a bad actor. To support this, we've added protected fence > +packet. This packet works by writing the a monotonically increasing value to > +a memory location that is only the privileged clients have write access to. > +User queues only have read access. When this packet is executed, the memory > +location is updated and other queues (kernel or user) can see the results. Does the driver handle this packet? I mean, does the driver insert it without the userspace request? What is the packet name? How can I find it in the kernel? > + > +Memory Management > +================= > + > +It is assumed that all buffers mapped into the GPUVM space for the process > are > +valid when engines on the GPU are running. The kernel driver will only allow > +user queues to run when all buffers are mapped. If there is a memory event > that > +requires buffer migration, the kernel driver will preempt the user queues, > +migrate buffers to where they need to be, update the GPUVM page tables and > +invaldidate the TLB, and then resume the user queues. > + > +Interaction with Kernel Queues > +============================== > + > +Depending on the IP and the scheduling firmware, you can enable kernel queues > +and user queues at the same time, However, you are limited by the HQD slots. /However/however/ > +Kernel queues are always mapped so any work the goes into kernel queues will > +take priority. This limits the available HQD slots for user queues. > + > +Not all IPs will support user queues on all GPUs. As such, UMDs will need to > +support both user queues and kernel queues depending on the IP. For > example, a > +GPU may support user queues for GFX, compute, and SDMA, but not for VCN, > JPEG, > +and VPE. UMDs need to support both. The kernel driver provides a way to > +determine if user queues and kernel queues are supported on a per IP basis. > +UMDs can query this information via the INFO IOCTL and determine whether to > use > +kernel queues or user queues for each IP. > + > +Queue Resets > +============ > + > +For most engines, queues can be reset individually. GFX, compute, and SDMA > +queues can be reset individually. When a hung queue is detected, it can be > +reset either via the scheduling firmware or MMIO. Since there are no kernel > +fences for most user queues, they will usually only be detected when some > other > +event happens; e.g., a memory event which requires migration of buffers. > When > +the queues are preempted, if the queue is hung, the preemption will fail. > +Driver will them look up the queues that failed to preempt and reset them and > +record which queues are hung. > + > + > +On the UMD side, we will add an USERQ QUERY_STATUS IOCTL to query the queue > +status. UMD will provide the queue id in the IOCTL and the kernel driver > +will check if it has already recorded the queue as hung (e.g., due to failed > +peemption) and report back the status. > + > +IOCTL Interfaces > +================ > + > +GPU virtual addresses used for queues and related data (rptrs, wptrs, context > +save areas, etc.) should be validated by the kernel mode driver to prevent > the > +user from specifying invalid GPU virtual addresses. If the user provides > +invalid GPU virtual addresses or doorbell indicies, the IOCTL should return > an > +error message. These buffers should also be tracked in the kernel driver so > +that if the user attempts to unmap the buffer(s) from the GPUVM, the umap > call > +would return an error. > + > +INFO > +---- > +There are several new INFO queries related to user queues in order to query > the > +size of user queue meta data needed for a user queue (e.g., context save > areas > +or shadow buffers), and whether kernel or user queues or both are supported > +for each IP type. > + > +USERQ > +----- > +The USERQ IOCTL is used for creating, freeing, and querying the status of > user > +queues. It supports 3 opcodes: > + > +1. CREATE - Create a user queue. The application provides a MQD-like > structure > + that devices the type of queue and associated metadata and flags for that > + queue type. Returns the queue id. > +2. FREE - Free a user queue. > +3. QUERY_STATRUS - Query that status of a queue. Used to check if the queue > is /QUERY_STATRUS/QUERY_STATUS/? Thanks Siqueira > + healthy or not. E.g., if the queue has been reset. (WIP) > + > +USERQ_SIGNAL > +------------ > +The USERQ_SIGNAL IOCTL is used to provide a list of sync objects to be > signaled. > + > +USERQ_WAIT > +---------- > +The USERQ_WAIT IOCTL is used to provide a list of sync object to be waited > on. > + > +Kernel and User Queues > +====================== > + > +In order to properly validate and test performance, we have a driver option > to > +select what type of queues are enabled (kernel queues, user queues or both). > +The user_queue driver parameter allows you to enable kernel queues only (0), > +user queues and kernel queues (1), and user queues only (2). Enabling user > +queues only will free up static queue assignments that would otherwise be > used > +by kernel queues for use by the scheduling firmware. Some kernel queues are > +required for kernel driver operation and they will always be created. When > the > +kernel queues are not enabled, they are not registered with the drm scheduler > +and the CS IOCTL will reject any incoming command submissions which target > those > +queue types. Kernel queues only mirrors the behavior on all existing GPUs. > +Enabling both queues allows for backwards compatibility with old userspace > while > +still supporting user queues. > -- > 2.49.0 > -- Rodrigo Siqueira
