netdev - Re: [PATCH net-next] net/mlx5: support software TX timestamp

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Message-ID: <CAL+tcoDu0NdZQ+QmqL9mF8VNj+4cPLgmy1maAucAc7JkKOjm6A@mail.gmail.com>
Date: Thu, 8 May 2025 14:42:57 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Tariq Toukan <ttoukan.linux@...il.com>
Cc: Stanislav Fomichev <stfomichev@...il.com>, netdev@...r.kernel.org, davem@...emloft.net, 
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com, saeedm@...dia.com, 
	tariqt@...dia.com, andrew+netdev@...n.ch, linux-rdma@...r.kernel.org, 
	linux-kernel@...r.kernel.org, leon@...nel.org, 
	Carolina Jubran <cjubran@...dia.com>
Subject: Re: [PATCH net-next] net/mlx5: support software TX timestamp

Hi Tariq,

On Thu, May 8, 2025 at 2:30 PM Tariq Toukan <ttoukan.linux@...il.com> wrote:
>
>
>
> On 07/05/2025 0:55, Stanislav Fomichev wrote:
> > Having a software timestamp (along with existing hardware one) is
> > useful to trace how the packets flow through the stack.
> > mlx5e_tx_skb_update_hwts_flags is called from tx paths
> > to setup HW timestamp; extend it to add software one as well.
> >
> > Signed-off-by: Stanislav Fomichev <stfomichev@...il.com>
> > ---
> >   drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c | 1 +
> >   drivers/net/ethernet/mellanox/mlx5/core/en_tx.c      | 1 +
> >   2 files changed, 2 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
> > index fdf9e9bb99ac..e399d7a3d6cb 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_ethtool.c
> > @@ -1689,6 +1689,7 @@ int mlx5e_ethtool_get_ts_info(struct mlx5e_priv *priv,
> >               return 0;
> >
> >       info->so_timestamping = SOF_TIMESTAMPING_TX_HARDWARE |
> > +                             SOF_TIMESTAMPING_TX_SOFTWARE |
> >                               SOF_TIMESTAMPING_RX_HARDWARE |
> >                               SOF_TIMESTAMPING_RAW_HARDWARE;
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
> > index 4fd853d19e31..f6dd26ad29e5 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
> > @@ -341,6 +341,7 @@ static void mlx5e_tx_skb_update_hwts_flags(struct sk_buff *skb)
> >   {
> >       if (unlikely(skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP))
> >               skb_shinfo(skb)->tx_flags |= SKBTX_IN_PROGRESS;
> > +     skb_tx_timestamp(skb);
>
> Doesn't this interfere with skb_tstamp_tx call in the completion flow
> (mlx5e_consume_skb)?

skb_tstamp_tx() only takes care of hardware timestamp in this case.

>
> What happens if both flags (SKBTX_SW_TSTAMP / SKBTX_HW_TSTAMP) are set
> Is it possible?

If only these two are set, only hardware timestamp will be passed to
the userspace because of the SOF_TIMESTAMPING_OPT_TX_SWHW limit in
__skb_tstamp_tx().

If users expect to see both timestamps, then
SOF_TIMESTAMPING_OPT_TX_SWHW has to be set.

Thanks,
Jason

>
> >   }
> >
> >   static void mlx5e_tx_check_stop(struct mlx5e_txqsq *sq)
>
>