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@xxxxxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxx>
