linux-kernel - RE: [Intel-wired-lan] [PATCH] i40e: drop useless bitmap_weight() call in i40e_set_rxfh

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Message-ID: <IA3PR11MB89865FF35893188BDF61B7FAE5ABA@IA3PR11MB8986.namprd11.prod.outlook.com>
Date: Wed, 17 Dec 2025 11:37:32 +0000
From: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
To: "Yury Norov (NVIDIA)" <yury.norov@...il.com>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "Kitszel, Przemyslaw"
	<przemyslaw.kitszel@...el.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>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [Intel-wired-lan] [PATCH] i40e: drop useless bitmap_weight() call
 in i40e_set_rxfh_fields()



> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf
> Of Yury Norov (NVIDIA)
> Sent: Tuesday, December 16, 2025 1:29 AM
> To: Nguyen, Anthony L <anthony.l.nguyen@...el.com>; Kitszel,
> Przemyslaw <przemyslaw.kitszel@...el.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>; intel-wired-lan@...ts.osuosl.org;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org
> Cc: Yury Norov (NVIDIA) <yury.norov@...il.com>
> Subject: [Intel-wired-lan] [PATCH] i40e: drop useless bitmap_weight()
> call in i40e_set_rxfh_fields()
> 
> bitmap_weight() is O(N) and useless here, because the following
> for_each_set_bit() returns immediately in case of empty flow_pctypes.
> 
> Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
> ---
>  .../net/ethernet/intel/i40e/i40e_ethtool.c    | 24 ++++++++----------
> -
>  1 file changed, 10 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> index f2c2646ea298..54b0348fdee3 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_ethtool.c
> @@ -3720,20 +3720,16 @@ static int i40e_set_rxfh_fields(struct
> net_device *netdev,
>  		return -EINVAL;
>  	}
> 
> -	if (bitmap_weight(flow_pctypes, FLOW_PCTYPES_SIZE)) {
> -		u8 flow_id;
> -
> -		for_each_set_bit(flow_id, flow_pctypes,
> FLOW_PCTYPES_SIZE) {
> -			i_setc = (u64)i40e_read_rx_ctl(hw,
> I40E_GLQF_HASH_INSET(0, flow_id)) |
> -				 ((u64)i40e_read_rx_ctl(hw,
> I40E_GLQF_HASH_INSET(1, flow_id)) << 32);
> -			i_set = i40e_get_rss_hash_bits(&pf->hw, nfc,
> i_setc);
> -
> -			i40e_write_rx_ctl(hw, I40E_GLQF_HASH_INSET(0,
> flow_id),
> -					  (u32)i_set);
> -			i40e_write_rx_ctl(hw, I40E_GLQF_HASH_INSET(1,
> flow_id),
> -					  (u32)(i_set >> 32));
> -			hena |= BIT_ULL(flow_id);
> -		}
> +	for_each_set_bit(flow_id, flow_pctypes, FLOW_PCTYPES_SIZE) {
You removed the flow_id declaration, but use it in the code below.
Are you sure it compiles?

> +		i_setc = (u64)i40e_read_rx_ctl(hw,
> I40E_GLQF_HASH_INSET(0, flow_id)) |
> +			 ((u64)i40e_read_rx_ctl(hw,
> I40E_GLQF_HASH_INSET(1, flow_id)) << 32);
> +		i_set = i40e_get_rss_hash_bits(&pf->hw, nfc, i_setc);
> +
> +		i40e_write_rx_ctl(hw, I40E_GLQF_HASH_INSET(0, flow_id),
> +				  (u32)i_set);
> +		i40e_write_rx_ctl(hw, I40E_GLQF_HASH_INSET(1, flow_id),
> +				  (u32)(i_set >> 32));
> +		hena |= BIT_ULL(flow_id);
>  	}
> 
>  	i40e_write_rx_ctl(hw, I40E_PFQF_HENA(0), (u32)hena);
> --
> 2.43.0