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Message-ID: <ZyN8xpq5C36Tg9rz@LouisNoVo>
Date: Thu, 31 Oct 2024 14:49:10 +0200
From: Louis Peens <louis.peens@...igine.com>
To: Caleb Sander Mateos <csander@...estorage.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	Arthur Kiyanovski <akiyano@...zon.com>,
	Brett Creeley <brett.creeley@....com>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Claudiu Manoil <claudiu.manoil@....com>,
	David Arinzon <darinzon@...zon.com>,
	"David S. Miller" <davem@...emloft.net>,
	Doug Berger <opendmb@...il.com>, Eric Dumazet <edumazet@...gle.com>,
	Eugenio PĂ©rez <eperezma@...hat.com>,
	Felix Fietkau <nbd@....name>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Geetha sowjanya <gakula@...vell.com>,
	hariprasad <hkelam@...vell.com>, Jakub Kicinski <kuba@...nel.org>,
	Jason Wang <jasowang@...hat.com>, Jonathan Corbet <corbet@....net>,
	Leon Romanovsky <leon@...nel.org>,
	Lorenzo Bianconi <lorenzo@...nel.org>,
	Mark Lee <Mark-MC.Lee@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Michael Chan <michael.chan@...adcom.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Noam Dagan <ndagan@...zon.com>, Paolo Abeni <pabeni@...hat.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Roy Pledge <Roy.Pledge@....com>, Saeed Bishara <saeedb@...zon.com>,
	Saeed Mahameed <saeedm@...dia.com>,
	Sean Wang <sean.wang@...iatek.com>,
	Shannon Nelson <shannon.nelson@....com>,
	Shay Agroskin <shayagr@...zon.com>, Simon Horman <horms@...nel.org>,
	Subbaraya Sundeep <sbhatta@...vell.com>,
	Sunil Goutham <sgoutham@...vell.com>, Tal Gilboa <talgi@...dia.com>,
	Tariq Toukan <tariqt@...dia.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	intel-wired-lan@...ts.osuosl.org,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, linux-rdma@...r.kernel.org,
	netdev@...r.kernel.org, oss-drivers@...igine.com,
	virtualization@...ts.linux.dev
Subject: Re: [resend PATCH 2/2] dim: pass dim_sample to net_dim() by reference

On Wed, Oct 30, 2024 at 06:23:26PM -0600, Caleb Sander Mateos wrote:
> net_dim() is currently passed a struct dim_sample argument by value.
> struct dim_sample is 24 bytes. Since this is greater 16 bytes, x86-64
> passes it on the stack. All callers have already initialized dim_sample
> on the stack, so passing it by value requires pushing a duplicated copy
> to the stack. Either witing to the stack and immediately reading it, or
> perhaps dereferencing addresses relative to the stack pointer in a chain
> of push instructions, seems to perform quite poorly.
> 
> In a heavy TCP workload, mlx5e_handle_rx_dim() consumes 3% of CPU time,
> 94% of which is attributed to the first push instruction to copy
> dim_sample on the stack for the call to net_dim():
> // Call ktime_get()
>   0.26 |4ead2:   call   4ead7 <mlx5e_handle_rx_dim+0x47>
> // Pass the address of struct dim in %rdi
>        |4ead7:   lea    0x3d0(%rbx),%rdi
> // Set dim_sample.pkt_ctr
>        |4eade:   mov    %r13d,0x8(%rsp)
> // Set dim_sample.byte_ctr
>        |4eae3:   mov    %r12d,0xc(%rsp)
> // Set dim_sample.event_ctr
>   0.15 |4eae8:   mov    %bp,0x10(%rsp)
> // Duplicate dim_sample on the stack
>  94.16 |4eaed:   push   0x10(%rsp)
>   2.79 |4eaf1:   push   0x10(%rsp)
>   0.07 |4eaf5:   push   %rax
> // Call net_dim()
>   0.21 |4eaf6:   call   4eafb <mlx5e_handle_rx_dim+0x6b>
> 
> To allow the caller to reuse the struct dim_sample already on the stack,
> pass the struct dim_sample by reference to net_dim().
> 
> Signed-off-by: Caleb Sander Mateos <csander@...estorage.com>
> ---
>  Documentation/networking/net_dim.rst                   |  2 +-
>  drivers/net/ethernet/amazon/ena/ena_netdev.c           |  2 +-
>  drivers/net/ethernet/broadcom/bcmsysport.c             |  2 +-
>  drivers/net/ethernet/broadcom/bnxt/bnxt.c              |  4 ++--
>  drivers/net/ethernet/broadcom/genet/bcmgenet.c         |  2 +-
>  drivers/net/ethernet/freescale/enetc/enetc.c           |  2 +-
>  drivers/net/ethernet/hisilicon/hns3/hns3_enet.c        |  4 ++--
>  drivers/net/ethernet/intel/ice/ice_txrx.c              |  4 ++--
>  drivers/net/ethernet/intel/idpf/idpf_txrx.c            |  4 ++--
>  drivers/net/ethernet/marvell/octeontx2/nic/otx2_txrx.c |  2 +-
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c            |  4 ++--
>  drivers/net/ethernet/mellanox/mlx5/core/en_txrx.c      |  4 ++--
>  drivers/net/ethernet/netronome/nfp/nfd3/dp.c           |  4 ++--
>  drivers/net/ethernet/netronome/nfp/nfdk/dp.c           |  4 ++--
>  drivers/net/ethernet/pensando/ionic/ionic_txrx.c       |  2 +-
>  drivers/net/virtio_net.c                               |  2 +-
>  drivers/soc/fsl/dpio/dpio-service.c                    |  2 +-
>  include/linux/dim.h                                    |  2 +-
>  lib/dim/net_dim.c                                      | 10 +++++-----
>  19 files changed, 31 insertions(+), 31 deletions(-)
> 
--- snip --

> diff --git a/drivers/net/ethernet/netronome/nfp/nfd3/dp.c b/drivers/net/ethernet/netronome/nfp/nfd3/dp.c
> index d215efc6cad0..f1c6c47564b1 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfd3/dp.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfd3/dp.c
> @@ -1177,11 +1177,11 @@ int nfp_nfd3_poll(struct napi_struct *napi, int budget)
>  			pkts = r_vec->rx_pkts;
>  			bytes = r_vec->rx_bytes;
>  		} while (u64_stats_fetch_retry(&r_vec->rx_sync, start));
>  
>  		dim_update_sample(r_vec->event_ctr, pkts, bytes, &dim_sample);
> -		net_dim(&r_vec->rx_dim, dim_sample);
> +		net_dim(&r_vec->rx_dim, &dim_sample);
>  	}
>  
>  	if (r_vec->nfp_net->tx_coalesce_adapt_on && r_vec->tx_ring) {
>  		struct dim_sample dim_sample = {};
>  		unsigned int start;
> @@ -1192,11 +1192,11 @@ int nfp_nfd3_poll(struct napi_struct *napi, int budget)
>  			pkts = r_vec->tx_pkts;
>  			bytes = r_vec->tx_bytes;
>  		} while (u64_stats_fetch_retry(&r_vec->tx_sync, start));
>  
>  		dim_update_sample(r_vec->event_ctr, pkts, bytes, &dim_sample);
> -		net_dim(&r_vec->tx_dim, dim_sample);
> +		net_dim(&r_vec->tx_dim, &dim_sample);
>  	}
>  
>  	return pkts_polled;
>  }
>  
> diff --git a/drivers/net/ethernet/netronome/nfp/nfdk/dp.c b/drivers/net/ethernet/netronome/nfp/nfdk/dp.c
> index dae5af7d1845..ebeb6ab4465c 100644
> --- a/drivers/net/ethernet/netronome/nfp/nfdk/dp.c
> +++ b/drivers/net/ethernet/netronome/nfp/nfdk/dp.c
> @@ -1287,11 +1287,11 @@ int nfp_nfdk_poll(struct napi_struct *napi, int budget)
>  			pkts = r_vec->rx_pkts;
>  			bytes = r_vec->rx_bytes;
>  		} while (u64_stats_fetch_retry(&r_vec->rx_sync, start));
>  
>  		dim_update_sample(r_vec->event_ctr, pkts, bytes, &dim_sample);
> -		net_dim(&r_vec->rx_dim, dim_sample);
> +		net_dim(&r_vec->rx_dim, &dim_sample);
>  	}
>  
>  	if (r_vec->nfp_net->tx_coalesce_adapt_on && r_vec->tx_ring) {
>  		struct dim_sample dim_sample = {};
>  		unsigned int start;
> @@ -1302,11 +1302,11 @@ int nfp_nfdk_poll(struct napi_struct *napi, int budget)
>  			pkts = r_vec->tx_pkts;
>  			bytes = r_vec->tx_bytes;
>  		} while (u64_stats_fetch_retry(&r_vec->tx_sync, start));
>  
>  		dim_update_sample(r_vec->event_ctr, pkts, bytes, &dim_sample);
> -		net_dim(&r_vec->tx_dim, dim_sample);
> +		net_dim(&r_vec->tx_dim, &dim_sample);
>  	}
>  
>  	return pkts_polled;
>  }
--- snip ---

Hi Caleb. Looks like a fair enough update to me in general, but I am not an
expert on 'dim'. For the corresponding nfp driver changes feel free to add:

Signed-off-by: Louis Peens <louis.peens@...igine.com>

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