On 27/02/2024 01:40, Niklas Söderlund wrote: > The RAVB device requires the SKB data to be aligned to 128 bytes. The > alignment is done by allocating a skb 128 bytes larger than the maximum > frame size supported by the device and adjusting the headroom to fit the > requirement. > > This code has been refactored a few times and small issues have been > added along the way. The issues are not harmful but prevents merging > parts of the Rx code which have been split in two implementations with > the addition of RZ/G2L support, a device that supports larger frame > sizes. > > This change removes the need for duplicated and somewhat inaccurate > hardware alignment constrains stored in the hardware information struct > by creating a helper to handle the allocation of a skb and alignment of > a skb data. > > For the R-Car class of devices the maximum frame size is 4K and each > descriptor is limited to 2K of data. The current implementation does not > support split descriptors, this limits the frame size to 2K. The > current hardware information however records the descriptor size just > under 2K due to bad understanding of the device when larger MTUs where > added. > > For the RZ/G2L device the maximum frame size is 8K and each descriptor > is limited to 4K of data. The current hardware information records this > correctly, but it gets the alignment constrains wrong as just aligns it > by 128, it does not extend it by 128 bytes to allow the full frame to be > stored. This works because the RZ/G2L device supports split descriptors > and allocates each skb to 8K and aligns each 4K descriptor in this > space. This change tidies up code which I re-wrote last week but I haven't sent patches yet... I was holding off sending further patches until we've completed gPTP testing, but maybe I can get an updated RFC series sent first then continue with testing. To get the best RX performance, we should allocate plain RX buffers using a page pool, then call build_skb() when a packet is received. Reducing RX buffer size from 8kB to 2kB for RZ/G2L gets me a 50% improvement in TCP RX throughput and a 200% improvement in UDP RX throughput. Using a page pool gets me a further 10% or so in both TCP & UDP RX throughput. So, if we merge this I'll be trying to remove ravb_alloc_skb() shortly anyway. So NACK on this for now, but let's co-ordinate the improvements we're both making so there aren't any merge conflicts for the maintainers to resolve. Thanks, -- Paul Barker
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