Hi, On Wed, Aug 12, 2015 at 10:42 PM, Boaz Harrosh <boaz@xxxxxxxxxxxxx> wrote: > On 08/12/2015 10:05 AM, Christoph Hellwig wrote: >> It turns out most DMA mapping implementation can handle SGLs without >> page structures with some fairly simple mechanical work. Most of it >> is just about consistently using sg_phys. For implementations that >> need to flush caches we need a new helper that skips these cache >> flushes if a entry doesn't have a kernel virtual address. >> >> However the ccio (parisc) and sba_iommu (parisc & ia64) IOMMUs seem >> to be operate mostly on virtual addresses. It's a fairly odd concept >> that I don't fully grasp, so I'll need some help with those if we want >> to bring this forward. >> >> Additional this series skips ARM entirely for now. The reason is >> that most arm implementations of the .map_sg operation just iterate >> over all entries and call ->map_page for it, which means we'd need >> to convert those to a ->map_pfn similar to Dan's previous approach. >> > [snip] > > It is a bit of work but is worth while, and accelerating tremendously > lots of workloads. Not like this abomination which only branches > things more and more, and making things fatter and slower. As a random guy reading a big bunch of patches on code I know almost nothing about, parts of this comment really resonated with me: overall, we seem to be adding a lot of if statements to code that appears to be in a hot path. I.e. ~90% of this patch set seems to be just mechanically dropping BUG_ON()s and converting open coded stuff to use accessor functions (which should be macros or get inlined, right?) - and the remaining bit is not flushing if we don't have a physical page somewhere. Would it make sense to split this patch set into a few bits: one to drop all the useless BUG_ON()s, one to convert all the open coded stuff to accessor functions, then another to do the actual page-less sg stuff? Thanks, -- Julian Calaby Email: julian.calaby@xxxxxxxxx Profile: http://www.google.com/profiles/julian.calaby/ -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
