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

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Message-ID: <bcb1b9e9-150d-38d1-d61e-2e0bf440d310@gmail.com>
Date:   Thu, 18 Oct 2018 18:51:56 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Francois Romieu <romieu@...zoreil.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        David Miller <davem@...emloft.net>,
        Realtek linux nic maintainers <nic_swsd@...ltek.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net] r8169: fix NAPI handling under high load



On 10/18/2018 03:59 PM, Francois Romieu wrote:
> Eric Dumazet <eric.dumazet@...il.com> :
> [...]
>> One has to wonder why rtl8169_poll(), which might be called in a loop under DOS,
>> has to call rtl_ack_events() ?
> 
> So as to cover a wider temporal range before any event can trigger an
> extra irq. I was more worried about irq cost than about IO cost (and
> I still am).
> 
Normally the IRQ would not be enabled under DOS.

Only when a poll would receive less packets than the budget
the following would normally allow the device to send another IRQ

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