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Date:   Fri, 8 May 2020 13:10:00 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Kevin Hao <haokexin@...il.com>
Cc:     Linux Netdev List <netdev@...r.kernel.org>,
        Sunil Goutham <sgoutham@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        hariprasad <hkelam@...vell.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] octeontx2-pf: Use the napi_alloc_frag() to alloc the pool buffers

On Fri, May 8, 2020 at 9:43 AM Kevin Hao <haokexin@...il.com> wrote:
>
> In the current codes, the octeontx2 uses its own method to allocate
> the pool buffers, but there are some issues in this implementation.
> 1. We have to run the otx2_get_page() for each allocation cycle and
>    this is pretty error prone. As I can see there is no invocation
>    of the otx2_get_page() in otx2_pool_refill_task(), this will leave
>    the allocated pages have the wrong refcount and may be freed wrongly.
> 2. It wastes memory. For example, if we only receive one packet in a
>    NAPI RX cycle, and then allocate a 2K buffer with otx2_alloc_rbuf()
>    to refill the pool buffers and leave the remain area of the allocated
>    page wasted. On a kernel with 64K page, 62K area is wasted.
>
> IMHO it is really unnecessary to implement our own method for the
> buffers allocate, we can reuse the napi_alloc_frag() to simplify
> our code.
>
> Signed-off-by: Kevin Hao <haokexin@...il.com>
> ---
>  .../marvell/octeontx2/nic/otx2_common.c       | 51 ++++++++-----------
>  .../marvell/octeontx2/nic/otx2_common.h       | 15 +-----
>  .../marvell/octeontx2/nic/otx2_txrx.c         |  3 +-
>  .../marvell/octeontx2/nic/otx2_txrx.h         |  4 --
>  4 files changed, 22 insertions(+), 51 deletions(-)
>
> diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> index f1d2dea90a8c..15fa1ad57f88 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
> @@ -379,40 +379,32 @@ void otx2_config_irq_coalescing(struct otx2_nic *pfvf, int qidx)
>                      (pfvf->hw.cq_ecount_wait - 1));
>  }
>
> -dma_addr_t otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool,
> -                          gfp_t gfp)
> +dma_addr_t _otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool)
>  {
>         dma_addr_t iova;
> +       u8 *buf;
>
> -       /* Check if request can be accommodated in previous allocated page */
> -       if (pool->page && ((pool->page_offset + pool->rbsize) <=
> -           (PAGE_SIZE << pool->rbpage_order))) {
> -               pool->pageref++;
> -               goto ret;
> -       }
> -
> -       otx2_get_page(pool);
> -
> -       /* Allocate a new page */
> -       pool->page = alloc_pages(gfp | __GFP_COMP | __GFP_NOWARN,
> -                                pool->rbpage_order);
> -       if (unlikely(!pool->page))
> +       buf = napi_alloc_frag(pool->rbsize);
> +       if (unlikely(!buf))
>                 return -ENOMEM;
>
> -       pool->page_offset = 0;
> -ret:
> -       iova = (u64)otx2_dma_map_page(pfvf, pool->page, pool->page_offset,
> -                                     pool->rbsize, DMA_FROM_DEVICE);
> -       if (!iova) {
> -               if (!pool->page_offset)
> -                       __free_pages(pool->page, pool->rbpage_order);
> -               pool->page = NULL;
> +       iova = dma_map_single(pfvf->dev, buf, pool->rbsize, DMA_FROM_DEVICE);
> +       if (unlikely(dma_mapping_error(pfvf->dev, iova)))
>                 return -ENOMEM;

Use DMA_ATTR_SKIP_CPU_SYNC while mapping the buffer.

Thanks,
Sunil.

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