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Date: Tue, 03 Nov 2020 16:35:01 -0800
From: Saeed Mahameed <saeed@...nel.org>
To: David Awogbemila <awogbemila@...gle.com>, netdev@...r.kernel.org
Cc: Catherine Sullivan <csully@...gle.com>,
Yangchun Fu <yangchun@...gle.com>
Subject: Re: [PATCH 4/4] gve: Add support for raw addressing in the tx path
On Tue, 2020-11-03 at 09:46 -0800, David Awogbemila wrote:
> From: Catherine Sullivan <csully@...gle.com>
>
> During TX, skbs' data addresses are dma_map'ed and passed to the NIC.
> This means that the device can perform DMA directly from these
> addresses
> and the driver does not have to copy the buffer content into
> pre-allocated buffers/qpls (as in qpl mode).
>
> Reviewed-by: Yangchun Fu <yangchun@...gle.com>
> Signed-off-by: Catherine Sullivan <csully@...gle.com>
> Signed-off-by: David Awogbemila <awogbemila@...gle.com>
> ---
> drivers/net/ethernet/google/gve/gve.h | 18 +-
> drivers/net/ethernet/google/gve/gve_adminq.c | 4 +-
> drivers/net/ethernet/google/gve/gve_desc.h | 8 +-
> drivers/net/ethernet/google/gve/gve_tx.c | 207 +++++++++++++++
> ----
> 4 files changed, 194 insertions(+), 43 deletions(-)
>
> static inline u32 gve_num_tx_qpls(struct gve_priv *priv)
> {
> - return priv->tx_cfg.num_queues;
> + if (priv->raw_addressing)
> + return 0;
> + else
> + return priv->tx_cfg.num_queues;
redundant else statement.
>
> -static void gve_dma_sync_for_device(struct device *dev, dma_addr_t
> *page_buses,
> +static void gve_dma_sync_for_device(struct gve_priv *priv,
> + dma_addr_t *page_buses,
> u64 iov_offset, u64 iov_len)
> {
> u64 last_page = (iov_offset + iov_len - 1) / PAGE_SIZE;
> u64 first_page = iov_offset / PAGE_SIZE;
> - dma_addr_t dma;
> u64 page;
>
> for (page = first_page; page <= last_page; page++) {
> - dma = page_buses[page];
> - dma_sync_single_for_device(dev, dma, PAGE_SIZE,
> DMA_TO_DEVICE);
> + dma_addr_t dma = page_buses[page];
> +
> + dma_sync_single_for_device(&priv->pdev->dev, dma,
> PAGE_SIZE, DMA_TO_DEVICE);
Why did you change the function params to pass priv here ?
I don't see any valid reason.
...
>
> - gve_dma_sync_for_device(dev, tx->tx_fifo.qpl->page_buses,
> + gve_dma_sync_for_device(priv, tx->tx_fifo.qpl->page_buses,
> info->iov[hdr_nfrags - 1].iov_offset,
> info->iov[hdr_nfrags - 1].iov_len);
>
...
> - gve_dma_sync_for_device(dev, tx->tx_fifo.qpl-
> >page_buses,
> + gve_dma_sync_for_device(priv, tx->tx_fifo.qpl-
> >page_buses,
> info->iov[i].iov_offset,
> info->iov[i].iov_len);
> copy_offset += info->iov[i].iov_len;
> @@ -472,6 +499,98 @@ static int gve_tx_add_skb(struct gve_tx_ring
> *tx, struct sk_buff *skb,
> return 1 + payload_nfrags;
> }
>
> +static int gve_tx_add_skb_no_copy(struct gve_priv *priv, struct
> gve_tx_ring *tx,
> + struct sk_buff *skb)
> +{
> + const struct skb_shared_info *shinfo = skb_shinfo(skb);
> + int hlen, payload_nfrags, l4_hdr_offset, seg_idx_bias;
> + union gve_tx_desc *pkt_desc, *seg_desc;
> + struct gve_tx_buffer_state *info;
> + bool is_gso = skb_is_gso(skb);
> + u32 idx = tx->req & tx->mask;
> + struct gve_tx_dma_buf *buf;
> + int last_mapped = 0;
> + u64 addr;
> + u32 len;
> + int i;
> +
> + info = &tx->info[idx];
> + pkt_desc = &tx->desc[idx];
> +
> + l4_hdr_offset = skb_checksum_start_offset(skb);
> + /* If the skb is gso, then we want only up to the tcp header in
> the first segment
> + * to efficiently replicate on each segment otherwise we want
> the linear portion
> + * of the skb (which will contain the checksum because skb-
> >csum_start and
> + * skb->csum_offset are given relative to skb->head) in the
> first segment.
> + */
> + hlen = is_gso ? l4_hdr_offset + tcp_hdrlen(skb) :
> + skb_headlen(skb);
> + len = skb_headlen(skb);
> +
> + info->skb = skb;
> +
> + addr = dma_map_single(tx->dev, skb->data, len, DMA_TO_DEVICE);
> + if (unlikely(dma_mapping_error(tx->dev, addr))) {
> + priv->dma_mapping_error++;
> + goto drop;
> + }
> + buf = &info->buf;
> + dma_unmap_len_set(buf, len, len);
> + dma_unmap_addr_set(buf, dma, addr);
> +
> + payload_nfrags = shinfo->nr_frags;
> + if (hlen < len) {
> + /* For gso the rest of the linear portion of the skb
> needs to
> + * be in its own descriptor.
> + */
> + payload_nfrags++;
> + gve_tx_fill_pkt_desc(pkt_desc, skb, is_gso,
> l4_hdr_offset,
> + 1 + payload_nfrags, hlen, addr);
> +
> + len -= hlen;
> + addr += hlen;
> + seg_desc = &tx->desc[(tx->req + 1) & tx->mask];
> + seg_idx_bias = 2;
> + gve_tx_fill_seg_desc(seg_desc, skb, is_gso, len, addr);
> + } else {
> + seg_idx_bias = 1;
> + gve_tx_fill_pkt_desc(pkt_desc, skb, is_gso,
> l4_hdr_offset,
> + 1 + payload_nfrags, hlen, addr);
> + }
> + idx = (tx->req + seg_idx_bias) & tx->mask;
> +
> + for (i = 0; i < payload_nfrags - (seg_idx_bias - 1); i++) {
> + const skb_frag_t *frag = &shinfo->frags[i];
> +
> + seg_desc = &tx->desc[idx];
> + len = skb_frag_size(frag);
> + addr = skb_frag_dma_map(tx->dev, frag, 0, len,
> DMA_TO_DEVICE);
> + if (unlikely(dma_mapping_error(tx->dev, addr))) {
> + priv->dma_mapping_error++;
don't you need to protect this from parallel access ?
> + goto unmap_drop;
> + }
> + buf = &tx->info[idx].buf;
> + tx->info[idx].skb = NULL;
> + dma_unmap_len_set(buf, len, len);
> + dma_unmap_addr_set(buf, dma, addr);
> +
> + gve_tx_fill_seg_desc(seg_desc, skb, is_gso, len, addr);
> + idx = (idx + 1) & tx->mask;
> + }
> +
> + return 1 + payload_nfrags;
> +
> +unmap_drop:
> + i--;
> + for (last_mapped = i + seg_idx_bias; last_mapped >= 0;
> last_mapped--) {
> + idx = (tx->req + last_mapped) & tx->mask;
> + gve_tx_unmap_buf(tx->dev, &tx->info[idx]);
> + }
> +drop:
> + tx->dropped_pkt++;
> + return 0;
> +}
> +
...
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