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Date: Fri, 20 Oct 2023 18:32:13 +0200
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Larysa Zaremba <larysa.zaremba@...el.com>
CC: <bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
<andrii@...nel.org>, <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
<john.fastabend@...il.com>, <kpsingh@...nel.org>, <sdf@...gle.com>,
<haoluo@...gle.com>, <jolsa@...nel.org>, David Ahern <dsahern@...il.com>,
Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn <willemb@...gle.com>,
Jesper Dangaard Brouer <hawk@...nel.org>, Anatoly Burakov
<anatoly.burakov@...el.com>, Alexander Lobakin <alexandr.lobakin@...el.com>,
Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan
<mtahhan@...hat.com>, <xdp-hints@...-project.net>, <netdev@...r.kernel.org>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>, Alexei Starovoitov
<alexei.starovoitov@...il.com>, Simon Horman <simon.horman@...igine.com>,
Tariq Toukan <tariqt@...lanox.com>, Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [PATCH bpf-next v6 11/18] ice: put XDP meta sources assignment
under a static key condition
On Thu, Oct 12, 2023 at 07:05:17PM +0200, Larysa Zaremba wrote:
> Usage of XDP hints requires putting additional information after the
> xdp_buff. In basic case, only the descriptor has to be copied on a
> per-packet basis, because xdp_buff permanently resides before per-ring
> metadata (cached time and VLAN protocol ID).
>
> However, in ZC mode, xdp_buffs come from a pool, so memory after such
> buffer does not contain any reliable information, so everything has to be
> copied, damaging the performance.
>
> Introduce a static key to enable meta sources assignment only when attached
> XDP program is device-bound.
>
> This patch eliminates a 6% performance drop in ZC mode, which was a result
> of addition of XDP hints to the driver.
>
> Signed-off-by: Larysa Zaremba <larysa.zaremba@...el.com>
> ---
> drivers/net/ethernet/intel/ice/ice.h | 1 +
> drivers/net/ethernet/intel/ice/ice_main.c | 14 ++++++++++++++
> drivers/net/ethernet/intel/ice/ice_txrx.c | 3 ++-
> drivers/net/ethernet/intel/ice/ice_xsk.c | 3 +++
> 4 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/intel/ice/ice.h b/drivers/net/ethernet/intel/ice/ice.h
> index 3d0f15f8b2b8..76d22be878a4 100644
> --- a/drivers/net/ethernet/intel/ice/ice.h
> +++ b/drivers/net/ethernet/intel/ice/ice.h
> @@ -210,6 +210,7 @@ enum ice_feature {
> };
>
> DECLARE_STATIC_KEY_FALSE(ice_xdp_locking_key);
> +DECLARE_STATIC_KEY_FALSE(ice_xdp_meta_key);
>
> struct ice_channel {
> struct list_head list;
> diff --git a/drivers/net/ethernet/intel/ice/ice_main.c b/drivers/net/ethernet/intel/ice/ice_main.c
> index 47e8920e1727..ee0df86d34b7 100644
> --- a/drivers/net/ethernet/intel/ice/ice_main.c
> +++ b/drivers/net/ethernet/intel/ice/ice_main.c
> @@ -48,6 +48,9 @@ MODULE_PARM_DESC(debug, "netif level (0=none,...,16=all)");
> DEFINE_STATIC_KEY_FALSE(ice_xdp_locking_key);
> EXPORT_SYMBOL(ice_xdp_locking_key);
>
> +DEFINE_STATIC_KEY_FALSE(ice_xdp_meta_key);
> +EXPORT_SYMBOL(ice_xdp_meta_key);
> +
> /**
> * ice_hw_to_dev - Get device pointer from the hardware structure
> * @hw: pointer to the device HW structure
> @@ -2634,6 +2637,11 @@ static int ice_xdp_alloc_setup_rings(struct ice_vsi *vsi)
> return -ENOMEM;
> }
>
> +static bool ice_xdp_prog_has_meta(struct bpf_prog *prog)
> +{
> + return prog && prog->aux->dev_bound;
> +}
> +
> /**
> * ice_vsi_assign_bpf_prog - set or clear bpf prog pointer on VSI
> * @vsi: VSI to set the bpf prog on
> @@ -2644,10 +2652,16 @@ static void ice_vsi_assign_bpf_prog(struct ice_vsi *vsi, struct bpf_prog *prog)
> struct bpf_prog *old_prog;
> int i;
>
> + if (ice_xdp_prog_has_meta(prog))
> + static_branch_inc(&ice_xdp_meta_key);
i thought boolean key would be enough but inc/dec should serve properly
for example prog hotswap cases.
> +
> old_prog = xchg(&vsi->xdp_prog, prog);
> ice_for_each_rxq(vsi, i)
> WRITE_ONCE(vsi->rx_rings[i]->xdp_prog, vsi->xdp_prog);
>
> + if (ice_xdp_prog_has_meta(old_prog))
> + static_branch_dec(&ice_xdp_meta_key);
> +
> if (old_prog)
> bpf_prog_put(old_prog);
> }
> diff --git a/drivers/net/ethernet/intel/ice/ice_txrx.c b/drivers/net/ethernet/intel/ice/ice_txrx.c
> index 4fd7614f243d..19fc182d1f4c 100644
> --- a/drivers/net/ethernet/intel/ice/ice_txrx.c
> +++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
> @@ -572,7 +572,8 @@ ice_run_xdp(struct ice_rx_ring *rx_ring, struct xdp_buff *xdp,
> if (!xdp_prog)
> goto exit;
>
> - ice_xdp_meta_set_desc(xdp, eop_desc);
> + if (static_branch_unlikely(&ice_xdp_meta_key))
My only concern is that we might be hurting in a minor way hints path now,
no?
> + ice_xdp_meta_set_desc(xdp, eop_desc);
>
> act = bpf_prog_run_xdp(xdp_prog, xdp);
> switch (act) {
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 39775bb6cec1..f92d7d33fde6 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -773,6 +773,9 @@ static void ice_prepare_pkt_ctx_zc(struct xdp_buff *xdp,
> union ice_32b_rx_flex_desc *eop_desc,
> struct ice_rx_ring *rx_ring)
> {
> + if (!static_branch_unlikely(&ice_xdp_meta_key))
> + return;
wouldn't it be better to pull it out and avoid calling
ice_prepare_pkt_ctx_zc() unnecessarily?
> +
> XSK_CHECK_PRIV_TYPE(struct ice_xdp_buff);
> ((struct ice_xdp_buff *)xdp)->pkt_ctx = rx_ring->pkt_ctx;
> ice_xdp_meta_set_desc(xdp, eop_desc);
> --
> 2.41.0
>
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