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

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Date:   Tue, 16 Oct 2018 23:17:31 +0200
From:   Holger Hoffstätte <holger@...lied-asynchrony.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 net] r8169: fix NAPI handling under high load

On 10/16/18 22:37, 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.

Very interesting! Could this be the reason for the mysterious
hangs & resets we experienced when enabling BQL for r8169?
They happened more often with TSO/GSO enabled and several people
attempted to fix those hangs unsuccessfully; it was later reverted
and has been since then (#87cda7cb43).
If this bug has been there "forever" it might be tempting to
re-apply BQL and see what happens. Any chance you could give that
a try? I'll gladly test patches, just like I'll run this one.

cheers
Holger