netdev - Re: [PATCH net-next 2/4] i40e: use generic unrolled

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Message-ID: <Z6nxUIK/xApn8B8N@boxer>
Date: Mon, 10 Feb 2025 13:30:08 +0100
From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>
CC: 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>, Alexei Starovoitov
	<ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, John Fastabend
	<john.fastabend@...il.com>, Andrii Nakryiko <andrii@...nel.org>, "Jose E.
 Marchesi" <jose.marchesi@...cle.com>, Toke
 Høiland-Jørgensen <toke@...hat.com>, Magnus Karlsson
	<magnus.karlsson@...el.com>, Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Jason Baron <jbaron@...mai.com>, Casey Schaufler <casey@...aufler-ca.com>,
	Nathan Chancellor <nathan@...nel.org>, <bpf@...r.kernel.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 2/4] i40e: use generic unrolled_count() macro

On Thu, Feb 06, 2025 at 07:26:27PM +0100, Alexander Lobakin wrote:
> i40e, as well as ice, has a custom loop unrolling macro for unrolling
> Tx descriptors filling on XSk xmit.
> Replace i40e defs with generic unrolled_count(), which is also more
> convenient as it allows passing defines as its argument, not hardcoded
> values, while the loop declaration will still be a usual for-loop.
> 
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>

Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>

> ---
>  drivers/net/ethernet/intel/i40e/i40e_xsk.h | 10 +---------
>  drivers/net/ethernet/intel/i40e/i40e_xsk.c |  4 +++-
>  2 files changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.h b/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> index ef156fad52f2..dd16351a7af8 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.h
> @@ -6,7 +6,7 @@
>  
>  #include <linux/types.h>
>  
> -/* This value should match the pragma in the loop_unrolled_for
> +/* This value should match the pragma in the unrolled_count()
>   * macro. Why 4? It is strictly empirical. It seems to be a good
>   * compromise between the advantage of having simultaneous outstanding
>   * reads to the DMA array that can hide each others latency and the
> @@ -14,14 +14,6 @@
>   */
>  #define PKTS_PER_BATCH 4
>  
> -#ifdef __clang__
> -#define loop_unrolled_for _Pragma("clang loop unroll_count(4)") for
> -#elif __GNUC__ >= 8
> -#define loop_unrolled_for _Pragma("GCC unroll 4") for
> -#else
> -#define loop_unrolled_for for
> -#endif
> -
>  struct i40e_ring;
>  struct i40e_vsi;
>  struct net_device;
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_xsk.c b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> index e28f1905a4a0..9f47388eaba5 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_xsk.c
> @@ -2,6 +2,7 @@
>  /* Copyright(c) 2018 Intel Corporation. */
>  
>  #include <linux/bpf_trace.h>
> +#include <linux/unroll.h>
>  #include <net/xdp_sock_drv.h>
>  #include "i40e_txrx_common.h"
>  #include "i40e_xsk.h"
> @@ -529,7 +530,8 @@ static void i40e_xmit_pkt_batch(struct i40e_ring *xdp_ring, struct xdp_desc *des
>  	dma_addr_t dma;
>  	u32 i;
>  
> -	loop_unrolled_for(i = 0; i < PKTS_PER_BATCH; i++) {
> +	unrolled_count(PKTS_PER_BATCH)
> +	for (i = 0; i < PKTS_PER_BATCH; i++) {
>  		u32 cmd = I40E_TX_DESC_CMD_ICRC | xsk_is_eop_desc(&desc[i]);
>  
>  		dma = xsk_buff_raw_get_dma(xdp_ring->xsk_pool, desc[i].addr);
> -- 
> 2.48.1
>