netdev - Re: [PATCH v5 5/7] r8169: Reduce spinlock contention for the start of RTL8117

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Message-ID: <459f8e54-419e-4e03-8c6c-250eba8889cc@gmail.com>
Date: Mon, 30 Oct 2023 14:51:43 +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 5/7] r8169: Reduce spinlock contention for the start of
 RTL8117

On 29.10.2023 19:36, Mirsad Goran Todorovac wrote:
> Repeated calls to r8168_mac_ocp_write() and r8168_mac_ocp_modify()
> in the startup of RTL8168ep involve implicit spin_lock_irqsave() and
> spin_unlock_irqrestore() on each invocation.
> 
> This is avoided by grouping unlocked __r8168_mac_ocp_write() and
> __r8168_mac_ocp_modify() primitives enclosed in the explicit
> spin_lock_irqsave()/spin_unlock_irqrestore() pair.
> 
> Even if the lock is not contended, the check requires a LOCK CMPXCHG
> or a similar instruction, which prevents all cores from accessing the
> memory bus.
> 
> Fixes: 1287723aa139b ("r8169: add support for RTL8117")
> 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 | 24 ++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/realtek/r8169_main.c b/drivers/net/ethernet/realtek/r8169_main.c
> index 27016aaeb6a0..50fbacb05953 100644
> --- a/drivers/net/ethernet/realtek/r8169_main.c
> +++ b/drivers/net/ethernet/realtek/r8169_main.c
> @@ -3348,7 +3348,15 @@ static void rtl_hw_start_8117(struct rtl8169_private *tp)
>  		{ 0x19, 0x0040,	0x1100 },
>  		{ 0x59, 0x0040,	0x1100 },
>  	};
> +
> +	static const struct e_info_regdata e_info_8117_wr_1[] = {
> +		{ 0xe63e, 0x0001 },
> +		{ 0xe63e, 0x0000 },
> +		{ 0xc094, 0x0000 },
> +		{ 0xc09e, 0x0000 },
> +	};
>  	int rg_saw_cnt;
> +	unsigned long flags;
>  
>  	rtl8168ep_stop_cmac(tp);
>  	rtl_ephy_init(tp, e_info_8117);
> @@ -3388,15 +3396,13 @@ static void rtl_hw_start_8117(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_write(tp, 0xea80, 0x0003);
> -	r8168_mac_ocp_modify(tp, 0xe052, 0x0000, 0x0009);
> -	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);
> +	raw_spin_lock_irqsave(&tp->mac_ocp_lock, flags);
> +	__r8168_mac_ocp_modify(tp, 0xe056, 0x00f0, 0x0070);
> +	__r8168_mac_ocp_write(tp, 0xea80, 0x0003);
> +	__r8168_mac_ocp_modify(tp, 0xe052, 0x0000, 0x0009);
> +	__r8168_mac_ocp_modify(tp, 0xd420, 0x0fff, 0x047f);
> +	__r8168_mac_ocp_write_seq(tp, e_info_8117_wr_1);
> +	raw_spin_unlock_irqrestore(&tp->mac_ocp_lock, flags);
>  
>  	/* firmware is for MAC only */
>  	r8169_apply_firmware(tp);

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