netdev - Re: [PATCH net-next v9 4/4] gve: Add support for raw addressing in the tx path

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Date:   Mon, 7 Dec 2020 10:15:46 -0800
From:   David Awogbemila <awogbemila@...gle.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Netdev <netdev@...r.kernel.org>, Saeed Mahameed <saeed@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Catherine Sullivan <csully@...gle.com>,
        Yangchun Fu <yangchun@...gle.com>
Subject: Re: [PATCH net-next v9 4/4] gve: Add support for raw addressing in
 the tx path

On Thu, Dec 3, 2020 at 10:16 AM Alexander Duyck
<alexander.duyck@...il.com> wrote:
>
> On Wed, Dec 2, 2020 at 10:24 AM David Awogbemila <awogbemila@...gle.com> 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         |  16 +-
> >  drivers/net/ethernet/google/gve/gve_adminq.c  |   4 +-
> >  drivers/net/ethernet/google/gve/gve_desc.h    |   8 +-
> >  drivers/net/ethernet/google/gve/gve_ethtool.c |   2 +
> >  drivers/net/ethernet/google/gve/gve_tx.c      | 197 ++++++++++++++----
> >  5 files changed, 185 insertions(+), 42 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/google/gve/gve.h b/drivers/net/ethernet/google/gve/gve.h
> > index 8aad4af2aa2b..9888fa92be86 100644
> > --- a/drivers/net/ethernet/google/gve/gve.h
> > +++ b/drivers/net/ethernet/google/gve/gve.h
> > @@ -112,12 +112,20 @@ struct gve_tx_iovec {
> >         u32 iov_padding; /* padding associated with this segment */
> >  };
> >
> > +struct gve_tx_dma_buf {
> > +       DEFINE_DMA_UNMAP_ADDR(dma);
> > +       DEFINE_DMA_UNMAP_LEN(len);
> > +};
> > +
> >  /* Tracks the memory in the fifo occupied by the skb. Mapped 1:1 to a desc
> >   * ring entry but only used for a pkt_desc not a seg_desc
> >   */
> >  struct gve_tx_buffer_state {
> >         struct sk_buff *skb; /* skb for this pkt */
> > -       struct gve_tx_iovec iov[GVE_TX_MAX_IOVEC]; /* segments of this pkt */
> > +       union {
> > +               struct gve_tx_iovec iov[GVE_TX_MAX_IOVEC]; /* segments of this pkt */
> > +               struct gve_tx_dma_buf buf;
> > +       };
> >  };
> >
> >  /* A TX buffer - each queue has one */
> > @@ -140,19 +148,23 @@ struct gve_tx_ring {
> >         __be32 last_nic_done ____cacheline_aligned; /* NIC tail pointer */
> >         u64 pkt_done; /* free-running - total packets completed */
> >         u64 bytes_done; /* free-running - total bytes completed */
> > +       u32 dropped_pkt; /* free-running - total packets dropped */
>
> Generally I would probably use a u64 for any count values. I'm not
> sure what rate you will be moving packets at but if something goes
> wrong you are better off with the counter not rolling over every few
> minutes.

Ok, using a u64 here would be better - I'll do that, thanks.

>
> >         /* Cacheline 2 -- Read-mostly fields */
> >         union gve_tx_desc *desc ____cacheline_aligned;
> >         struct gve_tx_buffer_state *info; /* Maps 1:1 to a desc */
> >         struct netdev_queue *netdev_txq;
> >         struct gve_queue_resources *q_resources; /* head and tail pointer idx */
> > +       struct device *dev;
> >         u32 mask; /* masks req and done down to queue size */
> > +       u8 raw_addressing; /* use raw_addressing? */
> >
> >         /* Slow-path fields */
> >         u32 q_num ____cacheline_aligned; /* queue idx */
> >         u32 stop_queue; /* count of queue stops */
> >         u32 wake_queue; /* count of queue wakes */
> >         u32 ntfy_id; /* notification block index */
> > +       u32 dma_mapping_error; /* count of dma mapping errors */
>
> Since this is a counter wouldn't it make more sense to place it up
> with the other counters?
>
> Looking over the rest of the patch it seems fine to me. The counters
> were the only thing that had me a bit concerned.

Ok, I'll use a u64 here and place it with the counter above.