Messages in this thread | | | Date | Fri, 20 May 2022 10:51:57 +0200 | From | Joerg Roedel <> | Subject | Re: [RFC PATCH] dma-iommu: Add iommu_dma_max_mapping_size() |
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On Wed, May 18, 2022 at 03:13:53PM +0200, Christoph Hellwig wrote: > On Tue, May 17, 2022 at 01:02:00PM +0100, Robin Murphy wrote: > >> So how to inform the SCSI driver of this caching limit then so that it may > >> limit the SGL length? > > > > Driver-specific mechanism; block-layer-specific mechanism; redefine this > > whole API to something like dma_opt_mapping_size(), as a limit above which > > mappings might become less efficient or start to fail (callback to my > > thoughts on [1] as well, I suppose); many options. Just not imposing a > > ridiculously low *maximum* on everyone wherein mapping calls "should not be > > larger than the returned value" when that's clearly bollocks. > > Well, for swiotlb it is a hard limit. So if we want to go down that > route we need two APIs, one for the optimal size and one for the > hard limit.
I agree with Robin, and if it really helps some drivers I am all for doing a dma_opt_mapping_size() instead. Limiting DMA mapping sizes to make drivers perform better gets a clear NAK from my side.
Regards,
Joerg
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