netdev - Re: [RFC PATCH v2 10/21] netgpu: add network/gpu/host dma module

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Date:   Tue, 28 Jul 2020 18:26:08 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     netdev@...r.kernel.org, kernel-team@...com
Subject: Re: [RFC PATCH v2 10/21] netgpu: add network/gpu/host dma module

On Mon, Jul 27, 2020 at 03:44:33PM -0700, Jonathan Lemon wrote:
> From: Jonathan Lemon <bsd@...com>
> 
> Netgpu provides a data path for zero-copy sends and receives
> without having the host CPU touch the data.  Protocol processing
> is done on the host CPU, while data is DMA'd to and from DMA
> mapped memory areas.  The initial code provides transfers between
> (mlx5 / host memory) and (mlx5 / nvidia GPU memory).
> 
> The use case for this module are GPUs used for machine learning,
> which are located near the NICs, and have a high bandwidth PCI
> connection between the GPU/NIC.

Do we have such a GPU driver in the kernel today?  We can't add new
apis/interfaces for no in-kernel users, as you well know.

There's lots of crazyness in this patch, but this is just really odd:

> +#if IS_MODULE(CONFIG_NETGPU)
> +#define MAYBE_EXPORT_SYMBOL(s)
> +#else
> +#define MAYBE_EXPORT_SYMBOL(s)	EXPORT_SYMBOL(s)
> +#endif

Why is that needed at all?  Why does no one else in the kernel need such
a thing?

And why EXPORT_SYMBOL() and not EXPORT_SYMBOL_GPL() (I have to ask).

thanks,

greg k-h