Re: [PATCH v4 1/5] dma-mapping: Add dma_opt_mapping_size()

[John Garry]

On 28/06/2022 12:23, Robin Murphy wrote:
> > +
> > +    size_t
> > +    dma_opt_mapping_size(struct device *dev);
> > +
> > +Returns the maximum optimal size of a mapping for the device. Mapping 
> > large
> > +buffers may take longer so device drivers are advised to limit total DMA
> > +streaming mappings length to the returned value.
>
> Nit: I'm not sure "advised" is necessarily the right thing to say in 
> general - that's only really true for a caller who cares about 
> throughput of churning through short-lived mappings more than anything 
> else, and doesn't take a significant hit overall from splitting up 
> larger requests. I do think it's good to clarify the exact context of 
> "optimal" here, but I'd prefer to be objectively clear that it's for 
> workloads where the up-front mapping overhead dominates.

Ok, sure, I can make that clear.

Thanks,
John