gpu-paging: Allow for more than one buffer to be swapped at a timertss22-aegpu-paging

This uses a very primitive linear disk sector allocation scheme.
Sectors are only reused when userspace resets assignment to 0 with
an NVGPU_AS_IOCTL_SWAP_RESET ioctl (which invalidates all current
swap buffers).

This sector assignment scheme is sufficient for use in a TimeWall-
like system, where all allocations are assumed to be static after
after task system release. This is not suitable for a system with
dynamic allocations, unless userspace manually resets swap state
regularly (benchmarks run a reset at start for example).

Support for dynamic allocations is on the backlog.

No significant speed impact.

Benchmarks, 100 iters, after:
gpu_paging_speed, write: 186.0ms +/- 3.51
gpu_paging_speed, read: 162.7ms +/- 2.58
gpu_paging_overhead_speed, write start: 35.4ms +/- 4.47
gpu_paging_overhead_speed, write finish: 3.3ms +/- 0.18
gpu_paging_overhead_speed, read start: 69.8ms +/- 6.42
gpu_paging_overhead_speed, read finish: 43.2ms +/- 0.91

1 files changed, 6 insertions, 1 deletions

diff --git a/include/uapi/linux/nvgpu.h b/include/uapi/linux/nvgpu.h
index b8ea59a1..08f8ecda 100644
--- a/include/uapi/linux/nvgpu.h
+++ b/include/uapi/linux/nvgpu.h
@@ -2214,9 +2214,14 @@ struct nvgpu_as_swap_buffer_args {
         _IOW(NVGPU_AS_IOCTL_MAGIC,  17, struct nvgpu_as_swap_buffer_args)
 #define NVGPU_AS_IOCTL_READ_SWAP_BUFFER_ASYNC_FINISH    \
         _IOW(NVGPU_AS_IOCTL_MAGIC,  18, struct nvgpu_as_swap_buffer_args)
+// Reset sector assignment to 0. Results in loss of all swapped data.
+// TODO: Don't require this - support dynamic task systems.
+#define NVGPU_AS_IOCTL_SWAP_RESET \
+        _IO(NVGPU_AS_IOCTL_MAGIC,  19)
+
 
 #define NVGPU_AS_IOCTL_LAST            \
-        _IOC_NR(NVGPU_AS_IOCTL_READ_SWAP_BUFFER_ASYNC_FINISH)
+        _IOC_NR(NVGPU_AS_IOCTL_SWAP_RESET)
 #define NVGPU_AS_IOCTL_MAX_ARG_SIZE     \
         sizeof(struct nvgpu_as_map_buffer_ex_args)