linux-kernel - Re: [PATCH net-next 2/2] mlx5/core: deduplicate {mlx5_,}eq_update

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Message-ID: <CADUfDZofFwy12oZYTmm3TE314RM79EGsxV6bKEBRMVFv8C3jNg@mail.gmail.com>
Date: Sun, 3 Nov 2024 14:18:43 -0800
From: Caleb Sander <csander@...estorage.com>
To: Parav Pandit <parav@...dia.com>
Cc: Saeed Mahameed <saeedm@...dia.com>, Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>, 
	Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, 
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] mlx5/core: deduplicate {mlx5_,}eq_update_ci()

On Sat, Nov 2, 2024 at 8:55 PM Parav Pandit <parav@...dia.com> wrote:
>
>
>
> > From: Caleb Sander Mateos <csander@...estorage.com>
> > Sent: Friday, November 1, 2024 9:17 AM
> >
> > The logic of eq_update_ci() is duplicated in mlx5_eq_update_ci(). The only
> > additional work done by mlx5_eq_update_ci() is to increment
> > eq->cons_index. Call eq_update_ci() from mlx5_eq_update_ci() to avoid
> > the duplication.
> >
> > Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
> > ---
> >  drivers/net/ethernet/mellanox/mlx5/core/eq.c | 9 +--------
> >  1 file changed, 1 insertion(+), 8 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> > b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> > index 859dcf09b770..078029c81935 100644
> > --- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> > +++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> > @@ -802,19 +802,12 @@ struct mlx5_eqe *mlx5_eq_get_eqe(struct
> > mlx5_eq *eq, u32 cc)  }  EXPORT_SYMBOL(mlx5_eq_get_eqe);
> >
> >  void mlx5_eq_update_ci(struct mlx5_eq *eq, u32 cc, bool arm)  {
> > -     __be32 __iomem *addr = eq->doorbell + (arm ? 0 : 2);
> > -     u32 val;
> > -
> >       eq->cons_index += cc;
> > -     val = (eq->cons_index & 0xffffff) | (eq->eqn << 24);
> > -
> > -     __raw_writel((__force u32)cpu_to_be32(val), addr);
> > -     /* We still want ordering, just not swabbing, so add a barrier */
> > -     wmb();
> > +     eq_update_ci(eq, arm);
> Long ago I had similar rework patches to get rid of __raw_writel(), which I never got chance to push,
>
> Eq_update_ci() is using full memory barrier.
> While mlx5_eq_update_ci() is using only write memory barrier.
>
> So it is not 100% deduplication by this patch.
> Please have a pre-patch improving eq_update_ci() to use wmb().
> Followed by this patch.

Right, patch 1/2 in this series is changing eq_update_ci() to use
writel() instead of __raw_writel() and avoid the memory barrier:
https://lore.kernel.org/lkml/20241101034647.51590-1-csander@purestorage.com/
Are you suggesting something different? If so, it would be great if
you could clarify what you mean.

Best,
Caleb