[RFC PATCH 0/3] Add an option for devices to skip SWIOTLB pre-copy on read.

[Andy Shevchenko]

On Tue, Feb 04, 2025 at 11:36:27PM +0000, Jianxiong Gao wrote:
> Removes an extra memory copy that occurs during IO read
> operations through the SWIOTLB. During high throughput
> read workloads, this extra copy is causing a lot of stress
> on the SWIOTLB.
> 
> With high performance devices, for example NVMe devices,
> the device will be overwriting the entire buffer.

Is this really guaranteed? I can imagine surprise power cut or
hotplug event, for example, just in the middle of the transfer.

> In such cases the entire pre-copy is redundent, only to slow down
> the overall bounce buffering.
> 
> We propose to add a full_buffer_write flag to the
> device_dma_parameters flag. When the flag is set the pre-copy
> can be omitted to boost performance.

-- 
With Best Regards,
Andy Shevchenko