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

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Message-ID: <20181016151708.3fff9bd9@xeon-e3>
Date:   Tue, 16 Oct 2018 15:17:08 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net] r8169: fix NAPI handling under high load

On Tue, 16 Oct 2018 22:37:31 +0200
Heiner Kallweit <hkallweit1@...il.com> 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.
> 
> This issue has been there more or less forever (at least it exists in
> 3.16 already), so I can't provide a "Fixes" tag. 
> 
> Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>

Another issue is this:

	if (work_done < budget) {
		napi_complete_done(napi, work_done);

		rtl_irq_enable(tp, enable_mask);
		mmiowb();
	}

	return work_done;
}


The code needs to check return value of napi_complete_done.

	if (work_done < budget &&
	    napi_complete_done(napi, work_done) {
		rtl_irq_enable(tp, enable_mask);
		mmiowb();
	}

	return work_done;
}

Try that, it might fix the problem and your logic would
be unnecessary