Re: [PATCH v2] gpudev: pin GPU memory

[Thomas Monjalon <thomas@monjalon.net>]

04/01/2022 03:41, eagostini@nvidia.com:
> From: Elena Agostini <eagostini@nvidia.com>
> 
> Enable the possibility to make a GPU memory area accessible from
> the CPU.
> 
> GPU memory has to be allocated via rte_gpu_mem_alloc().
> 
> This patch allows the gpudev library to pin, through the GPU driver,
> a chunk of GPU memory and to return a memory pointer usable
> by the CPU to access the GPU memory area.
> 
> Signed-off-by: Elena Agostini <eagostini@nvidia.com>
[...]
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Pin a chunk of GPU memory to make it accessible from the CPU

You should define what means "pin" exactly.
Which properties should we expect?

> + * using the memory pointer returned by the function.

Which function should return the pointer?
rte_gpu_mem_pin is returning an int.


> + * GPU memory has to be allocated via rte_gpu_mem_alloc().

Why pinning is not done by rte_gpu_mem_alloc()?
Should it be a flag?

> + *
> + * @param dev_id
> + *   Device ID requiring pinned memory.
> + * @param size
> + *   Number of bytes to pin.
> + *   Requesting 0 will do nothing.
> + * @param ptr
> + *   Pointer to the GPU memory area to be pinned.
> + *   NULL is a no-op accepted value.
> +
> + * @return
> + *   A pointer to the pinned GPU memory usable by the CPU, otherwise NULL and rte_errno is set:
> + *   - ENODEV if invalid dev_id
> + *   - EINVAL if reserved flags

Which reserved flags?

> + *   - ENOTSUP if operation not supported by the driver
> + *   - E2BIG if size is higher than limit
> + *   - ENOMEM if out of space

Is out of space relevant for pinning?

> + *   - EPERM if driver error
> + */
> +__rte_experimental
> +int rte_gpu_mem_pin(int16_t dev_id, size_t size, void *ptr);