Abstract: One embodiment of the present invention includes techniques to support demand paging across a processing unit. Before a host unit transmits a command to an engine that does not tolerate page faults, the host unit ensures that the virtual memory addresses associated with the command are appropriately mapped to physical memory addresses. In particular, if the virtual memory addresses are not appropriately mapped, then the processing unit performs actions to map the virtual memory address to appropriate locations in physical memory. Further, the processing unit ensures that the access permissions required for successful execution of the command are established. Because the virtual memory address mappings associated with the command are valid when the engine receives the command, the engine does not encounter page faults upon executing the command. Consequently, in contrast to prior-art techniques, the engine supports demand paging regardless of whether the engine is involved in remedying page faults.

Abstract: One embodiment of the present invention sets forth a graphics processing system. The graphics processing system includes a screen-space pipeline and a tiling unit. The screen-space pipeline is configured to perform visibility testing and fragment shading. The tiling unit is configured to determine that a first set of primitives overlaps a first cache tile. The tiling unit is also configured to first transmit the first set of primitives to the screen-space pipeline with a command configured to cause the screen-space pipeline to process the first set of primitives in a z-only mode, and then transmit the first set of primitives to the screen-space pipeline with a command configured to cause the screen-space pipeline to process the first set of primitives in a normal mode. In the z-only mode, at least some fragment shading operations are disabled in the screen-space pipeline. In the normal mode, fragment shading operations are enabled.

Abstract: One embodiment of the present invention is a memory subsystem that includes a sliding window tracker that tracks memory accesses associated with a sliding window of memory page groups. When the sliding window tracker detects an access operation associated with a memory page group within the sliding window, the sliding window tracker sets a reference bit that is associated with the memory page group and is included in a reference vector that represents accesses to the memory page groups within the sliding window. Based on the values of the reference bits, the sliding window tracker causes the selection a memory page in a memory page group that has fallen into disuse from a first memory to a second memory. Because the sliding window tracker tunes the memory pages that are resident in the first memory to reflect memory access patterns, the overall performance of the memory subsystem is improved.

Abstract: Techniques are disclosed for tracking memory page accesses in a unified virtual memory system. An access tracking unit detects a memory page access generated by a first processor for accessing a memory page in a memory system of a second processor. The access tracking unit determines whether a cache memory includes an entry for the memory page. If so, then the access tracking unit increments an associated access counter. Otherwise, the access tracking unit attempts to find an unused entry in the cache memory that is available for allocation. If so, then the access tracking unit associates the second entry with the memory page, and sets an access counter associated with the second entry to an initial value. Otherwise, the access tracking unit selects a valid entry in the cache memory; clears an associated valid bit; associates the entry with the memory page; and initializes an associated access counter.

Abstract: A technique for simultaneously executing multiple tasks, each having an independent virtual address space, involves assigning an address space identifier (ASID) to each task and constructing each virtual memory access request to include both a virtual address and the ASID. During virtual to physical address translation, the ASID selects a corresponding page table, which includes virtual to physical address mappings for the ASID and associated task. Entries for a translation look-aside buffer (TLB) include both the virtual address and ASID to complete each mapping to a physical address. Deep scheduling of tasks sharing a virtual address space may be implemented to improve cache affinity for both TLB and data caches.

Abstract: A system for managing virtual memory. The system includes a first processing unit configured to execute a first operation that references a first virtual memory address. The system also includes a first memory management unit (MMU) associated with the first processing unit and configured to generate a first page fault upon determining that a first page table that is stored in a first memory unit associated with the first processing unit does not include a mapping corresponding to the first virtual memory address. The system further includes a first copy engine associated with the first processing unit. The first copy engine is configured to read a first command queue to determine a first mapping that corresponds to the first virtual memory address and is included in a first page state directory. The first copy engine is also configured to update the first page table to include the first mapping.

Abstract: One embodiment of the present invention sets forth a technique for error-checking a compute task. The technique involves receiving a pointer to a compute task, storing the pointer in a scheduling queue, determining that the compute task should be executed, retrieving the pointer from the scheduling queue, determining via an error-check procedure that the compute task is eligible for execution, and executing the compute task.

Abstract: Techniques are disclosed for storing post-z coverage data in a render target. A color raster operations (CROP) unit receives a coverage mask associated with a portion of a graphics primitive, where the graphics primitive intersects a pixel that includes a multiple samples, and the portion covers at least one sample. The CROP unit stores the coverage mask in a data field in the render target at a location associated with the pixel. One advantage of the disclosed techniques is that the GPU computes color and other pixel information only for visible fragments as determined by post-z coverage data. The GPU does not compute color and other pixel information for obscured fragments, thereby reducing overall power consumption and improving overall render performance.

Abstract: One embodiment of the present invention sets forth a graphics processing system. The graphics processing system includes a screen-space pipeline and a tiling unit. The screen-space pipeline is configured to perform visibility testing and fragment shading. The tiling unit is configured to determine that a first set of primitives overlaps a first cache tile. The tiling unit is also configured to first transmit the first set of primitives to the screen-space pipeline with a command configured to cause the screen-space pipeline to process the first set of primitives in a z-only mode, and then transmit the first set of primitives to the screen-space pipeline with a command configured to cause the screen-space pipeline to process the first set of primitives in a normal mode. In the z-only mode, at least some fragment shading operations are disabled in the screen-space pipeline. In the normal mode, fragment shading operations are enabled.

Abstract: Techniques are disclosed for tracking memory page accesses in a unified virtual memory system. An access tracking unit detects a memory page access generated by a first processor for accessing a memory page in a memory system of a second processor. The access tracking unit determines whether a cache memory includes an entry for the memory page. If so, then the access tracking unit increments an associated access counter. Otherwise, the access tracking unit attempts to find an unused entry in the cache memory that is available for allocation. If so, then the access tracking unit associates the second entry with the memory page, and sets an access counter associated with the second entry to an initial value. Otherwise, the access tracking unit selects a valid entry in the cache memory; clears an associated valid bit; associates the entry with the memory page; and initializes an associated access counter.

Abstract: Techniques are disclosed for tracking memory page accesses in a unified virtual memory system. An access tracking unit detects a memory page access generated by a first processor for accessing a memory page in a memory system of a second processor. The access tracking unit determines whether a cache memory includes an entry for the memory page. If so, then the access tracking unit increments an associated access counter. Otherwise, the access tracking unit attempts to find an unused entry in the cache memory that is available for allocation. If so, then the access tracking unit associates the second entry with the memory page, and sets an access counter associated with the second entry to an initial value. Otherwise, the access tracking unit selects a valid entry in the cache memory; clears an associated valid bit; associates the entry with the memory page; and initializes an associated access counter.

Abstract: One embodiment of the present invention includes a microcontroller coupled to a memory management unit (MMU). The MMU is coupled to a page table included in a physical memory, and the microcontroller is configured to perform one or more virtual memory operations associated with the physical memory and the page table. In operation, the microcontroller receives a page fault generated by the MMU in response to an invalid memory access via a virtual memory address. To remedy such a page fault, the microcontroller performs actions to map the virtual memory address to an appropriate location in the physical memory. By contrast, in prior-art systems, a fault handler would typically remedy the page fault. Advantageously, because the microcontroller executes these tasks locally with respect to the MMU and the physical memory, latency associated with remedying page faults may be decreased. Consequently, overall system performance may be increased.

Abstract: Embodiments of the approaches disclosed herein include a subsystem that includes an access tracking mechanism configured to monitor access operations directed to a first memory and a second memory. The access tracking mechanism detects an access operation generated by a processor for accessing a first memory page residing on the second memory. The access tracking mechanism further determines that the first memory page is included in a first subset of memory pages residing on the second memory. The access tracking mechanism further locates, within a reference vector, a reference bit that corresponds to the first memory page, and sets the reference bit. One advantage of the present invention is that memory pages in a hybrid system migrate as needed to increase overall memory performance.

Abstract: One embodiment of the present invention includes techniques for a first processing unit to perform an atomic operation on a memory page shared with a second processing unit. The memory page is associated with a page table entry corresponding to the first processing unit. Before executing the atomic operation, an MMU included in the first processing unit evaluates an atomic permission bit that is included in the page table entry. If the MMU determines that the atomic permission bit is inactive, then the two processing units coordinate to change the permission status of the memory page. As part of the status change, the atomic permission bit in the page table entry is activated. Subsequently, the first processing unit performs the atomic operation uninterrupted by the second processing unit. Advantageously, coordinating the processing unit via the atomic permission bit ensures the proper and efficient execution of the atomic operation.

Abstract: One embodiment of the present invention is a parallel processing unit (PPU) that includes one or more streaming multiprocessors (SMs) and implements a replay unit per SM. Upon detecting a page fault associated with a memory transaction issued by a particular SM, the corresponding replay unit causes the SM, but not any unaffected SMs, to cease issuing new memory transactions. The replay unit then stores the faulting memory transaction and any faulting in-flight memory transaction in a replay buffer. As page faults are resolved, the replay unit replays the memory transactions in the replay buffer—removing successful memory transactions from the replay buffer—until all of the stored memory transactions have successfully executed. Advantageously, the overall performance of the PPU is improved compared to conventional PPUs that, upon detecting a page fault, stop performing memory transactions across all SMs included in the PPU until the fault is resolved.

Abstract: A system for managing virtual memory. The system includes a first processing unit configured to execute a first operation that references a first virtual memory address. The system also includes a first memory management unit (MMU) associated with the first processing unit and configured to generate a first page fault upon determining that a first page table that is stored in a first memory unit associated with the first processing unit does not include a mapping corresponding to the first virtual memory address. The system further includes a first copy engine associated with the first processing unit. The first copy engine is configured to read a first command queue to determine a first mapping that corresponds to the first virtual memory address and is included in a first page state directory. The first copy engine is also configured to update the first page table to include the first mapping.

Abstract: One embodiment of the present invention sets forth a computer-implemented method for migrating a memory page from a first memory to a second memory. The method includes determining a first page size supported by the first memory. The method also includes determining a second page size supported by the second memory. The method further includes determining a use history of the memory page based on an entry in a page state directory associated with the memory page. The method also includes migrating the memory page between the first memory and the second memory based on the first page size, the second page size, and the use history.

Abstract: One embodiment of the present invention includes a microcontroller coupled to a memory management unit (MMU). The MMU is coupled to a page table included in a physical memory, and the microcontroller is configured to perform one or more virtual memory operations associated with the physical memory and the page table. In operation, the microcontroller receives a page fault generated by the MMU in response to an invalid memory access via a virtual memory address. To remedy such a page fault, the microcontroller performs actions to map the virtual memory address to an appropriate location in the physical memory. By contrast, in prior-art systems, a fault handler would typically remedy the page fault. Advantageously, because the microcontroller executes these tasks locally with respect to the MMU and the physical memory, latency associated with remedying page faults may be decreased. Consequently, overall system performance may be increased.

Abstract: A system for managing virtual memory. The system includes a first processing unit configured to execute a first operation that references a first virtual memory address. The system also includes a first memory management unit (MMU) associated with the first processing unit and configured to generate a first page fault upon determining that a first page table that is stored in a first memory unit associated with the first processing unit does not include a mapping corresponding to the first virtual memory address. The system further includes a first copy engine associated with the first processing unit. The first copy engine is configured to read a first command queue to determine a first mapping that corresponds to the first virtual memory address and is included in a first page state directory. The first copy engine is also configured to update the first page table to include the first mapping.

Abstract: A system for managing virtual memory. The system includes a first processing unit configured to execute a first operation that references a first virtual memory address. The system also includes a first memory management unit (MMU) associated with the first processing unit and configured to generate a first page fault upon determining that a first page table that is stored in a first memory unit associated with the first processing unit does not include a mapping corresponding to the first virtual memory address. The system further includes a first copy engine associated with the first processing unit. The first copy engine is configured to read a first command queue to determine a first mapping that corresponds to the first virtual memory address and is included in a first page state directory. The first copy engine is also configured to update the first page table to include the first mapping.