netdev - Re: [PATCH v2 net] r8169: fix NAPI handling under high load

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Date:   Thu, 18 Oct 2018 11:02:02 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] r8169: fix NAPI handling under high load



On 10/18/2018 10:56 AM, Heiner Kallweit wrote:
> rtl_rx() and rtl_tx() are called only if the respective bits are set
> in the interrupt status register. Under high load NAPI may not be
> able to process all data (work_done == budget) and it will schedule
> subsequent calls to the poll callback.
> rtl_ack_events() however resets the bits in the interrupt status
> register, therefore subsequent calls to rtl8169_poll() won't call
> rtl_rx() and rtl_tx() - chip interrupts are still disabled.
> 
> Fix this by calling rtl_rx() and rtl_tx() independent of the bits
> set in the interrupt status register. Both functions will detect
> if there's nothing to do for them.
> 
> Fixes: da78dbff2e05 ("r8169: remove work from irq handler.")
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
> ---
> v2:
> - added "Fixes" tag
> ---
>  drivers/net/ethernet/realtek/r8169.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/realtek/r8169.c b/drivers/net/ethernet/realtek/r8169.c
> index 8c4f49adc..7caf3b7e9 100644
> --- a/drivers/net/ethernet/realtek/r8169.c
> +++ b/drivers/net/ethernet/realtek/r8169.c
> @@ -6528,17 +6528,15 @@ static int rtl8169_poll(struct napi_struct *napi, int budget)
>  	struct rtl8169_private *tp = container_of(napi, struct rtl8169_private, napi);
>  	struct net_device *dev = tp->dev;
>  	u16 enable_mask = RTL_EVENT_NAPI | tp->event_slow;
> -	int work_done= 0;
> +	int work_done;
>  	u16 status;
>  
>  	status = rtl_get_events(tp);
>  	rtl_ack_events(tp, status & ~tp->event_slow);
>  
> -	if (status & RTL_EVENT_NAPI_RX)
> -		work_done = rtl_rx(dev, tp, (u32) budget);
> +	work_done = rtl_rx(dev, tp, (u32) budget);
>  
> -	if (status & RTL_EVENT_NAPI_TX)
> -		rtl_tx(dev, tp);
> +	rtl_tx(dev, tp);
>  
>  	if (status & tp->event_slow) {
>  		enable_mask &= ~tp->event_slow;
> 

One has to wonder why rtl8169_poll(), which might be called in a loop under DOS,
has to call rtl_ack_events() ?

Should not this be called one time from hard irq handler instead ?