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

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Message-ID: <aUNK6So7KzD3zngt@yury>
Date: Wed, 17 Dec 2025 19:29:29 -0500
From: Yury Norov <yury.norov@...il.com>
To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>
Cc: "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()

On Wed, Dec 17, 2025 at 11:37:32AM +0000, Loktionov, Aleksandr wrote:
> 
> 
> > -----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?

No it doesn't. I'll send the right version shortly. Sorry for this
noise.

Thanks,
Yury