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

From: John Garry
Date: Tue Jun 28 2022 - 07:28:25 EST


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