linux-kernel - Re: [PATCH v5 3/7] r8169: Coalesce mac ocp write and modify for 8168H start to reduce spinlock contention

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Message-ID: <a3cc5420-8b0e-4336-accd-78557b5f8f46@gmail.com>
Date:   Mon, 30 Oct 2023 14:50:36 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
        Jason Gunthorpe <jgg@...pe.ca>, Joerg Roedel <jroedel@...e.de>,
        Lu Baolu <baolu.lu@...ux.intel.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Cc:     Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, nic_swsd@...ltek.com,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Marco Elver <elver@...gle.com>
Subject: Re: [PATCH v5 3/7] r8169: Coalesce mac ocp write and modify for 8168H
 start to reduce spinlock contention

On 29.10.2023 19:35, Mirsad Goran Todorovac wrote:
> Repeated calls to r8168_mac_ocp_write() and r8168_mac_ocp_modify() in
> the startup of 8168H involve implicit spin_lock_irqsave() and spin_unlock_irqrestore()
> on each invocation.
> 
> Coalesced with the corresponding helpers into r8168_mac_ocp_write_seq() and
> r8168_mac_ocp_modify_seq() with a sinqle paired spin_lock_irqsave() and
> spin_unlock_irqrestore(), these calls help reduce overall spinlock contention.
> 
> Fixes: ef712ede3541d ("r8169: add helper r8168_mac_ocp_modify")
> Fixes: 6e1d0b8988188 ("r8169:add support for RTL8168H and RTL8107E")
> Cc: Heiner Kallweit <hkallweit1@...il.com>
> Cc: Marco Elver <elver@...gle.com>
> Cc: nic_swsd@...ltek.com
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: netdev@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Link: https://lore.kernel.org/lkml/20231028005153.2180411-1-mirsad.todorovac@alu.unizg.hr/
> Link: https://lore.kernel.org/lkml/20231028110459.2644926-1-mirsad.todorovac@alu.unizg.hr/
> Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
> ---
> v5:
>  added unlocked primitives to allow mac ocs modify grouping
>  applied coalescing of mac ocp writes/modifies for 8168ep and 8117
>  some formatting fixes to please checkpatch.pl
> 
> v4:
>  fixed complaints as advised by Heiner and checkpatch.pl
>  split the patch into five sections to be more easily manipulated and reviewed
>  introduced r8168_mac_ocp_write_seq()
>  applied coalescing of mac ocp writes/modifies for 8168H, 8125 and 8125B
> 
> v3:
>  removed register/mask pair array sentinels, so using ARRAY_SIZE().
>  avoided duplication of RTL_W32() call code as advised by Heiner.
> 
>  drivers/net/ethernet/realtek/r8169_main.c | 26 +++++++++++++++--------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
> index f4a1d1a74b8b..29ee93b8b702 100644
> --- a/drivers/net/ethernet/realtek/r8169_main.c
> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> @@ -3231,6 +3231,21 @@ static void rtl_hw_start_8168h_1(struct rtl8169_private *tp)
>  		{ 0x04, 0xffff,	0x854a },
>  		{ 0x01, 0xffff,	0x068b }
>  	};
> +
> +	static const struct e_info_regmaskset e_info_regmaskset_8168h_1[] = {
> +		{ 0xe056, 0x00f0, 0x0070 },
> +		{ 0xe052, 0x6000, 0x8008 },
> +		{ 0xe0d6, 0x01ff, 0x017f },
> +		{ 0xd420, 0x0fff, 0x047f },
> +	};
> +
> +	static const struct e_info_regdata e_info_regdata_8168h_1[] = {
> +		{ 0xe63e, 0x0001 },
> +		{ 0xe63e, 0x0000 },
> +		{ 0xc094, 0x0000 },
> +		{ 0xc09e, 0x0000 },
> +	};
> +
>  	int rg_saw_cnt;
>  
>  	rtl_ephy_init(tp, e_info_8168h_1);
> @@ -3271,15 +3286,8 @@ static void rtl_hw_start_8168h_1(struct rtl8169_private *tp)
>  		r8168_mac_ocp_modify(tp, 0xd412, 0x0fff, sw_cnt_1ms_ini);
>  	}
>  
> -	r8168_mac_ocp_modify(tp, 0xe056, 0x00f0, 0x0070);
> -	r8168_mac_ocp_modify(tp, 0xe052, 0x6000, 0x8008);
> -	r8168_mac_ocp_modify(tp, 0xe0d6, 0x01ff, 0x017f);
> -	r8168_mac_ocp_modify(tp, 0xd420, 0x0fff, 0x047f);
> -
> -	r8168_mac_ocp_write(tp, 0xe63e, 0x0001);
> -	r8168_mac_ocp_write(tp, 0xe63e, 0x0000);
> -	r8168_mac_ocp_write(tp, 0xc094, 0x0000);
> -	r8168_mac_ocp_write(tp, 0xc09e, 0x0000);
> +	r8168_mac_ocp_modify_seq(tp, e_info_regmaskset_8168h_1);
> +	r8168_mac_ocp_write_seq(tp, e_info_regdata_8168h_1);
>  }
>  
>  static void rtl_hw_start_8168ep(struct rtl8169_private *tp)

For these few calls I don't really see a benefit in the change.
Instead it makes the code harder to read.