On Mon, Jul 31, 2023 at 11:00 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > On Mon, 31 Jul 2023 19:47:08 +0200 Jesper Dangaard Brouer wrote: > > > This should be smaller than PAGE_SIZE only if you're wasting the rest > > > of the buffer, e.g. MTU is 3k so you know last 1k will never get used. > > > PAGE_SIZE is always a multiple of BNXT_RX_PAGE so you waste nothing. > > > > Remember pp.max_len is used for dma_sync_for_device. > > If driver is smart, it can set pp.max_len according to MTU, as the (DMA > > sync for) device knows hardware will not go beyond this. > > On Intel "dma_sync_for_device" is a no-op, so most drivers done > > optimized for this. I remember is had HUGE effects on ARM EspressoBin board. > > Note that (AFAIU) there is no MTU here, these are pages for LRO/GRO, > they will be filled with TCP payload start to end. page_pool_put_page() > does nothing for non-last frag, so we'll only sync for the last > (BNXT_RX_PAGE-sized) frag released, and we need to sync the entire > host page. Correct, there is no MTU here. Remember this matters only when PAGE_SIZE > BNXT_RX_PAGE_SIZE (e.g. 64K PAGE_SIZE and 32K BNXT_RX_PAGE_SIZE). I think we want to dma_sync_for_device for 32K in this case.
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