netdev - Re: [PATCH net] ixgbe: check return value of napi_complete

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Date:   Fri, 21 Sep 2018 06:33:18 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Song Liu <songliubraving@...com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        netdev <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        Kernel Team <Kernel-team@...com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH net] ixgbe: check return value of napi_complete_done()



On 09/21/2018 12:17 AM, Song Liu wrote:
> 
> 
>> On Sep 20, 2018, at 4:49 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>>
>>
>> On 09/20/2018 04:43 PM, Song Liu wrote:
>>>
>>
>>> I tried to totally skip ndo_poll_controller() here. It did avoid hitting
>>> the issue. However, netpoll will drop (fail to send) more packets. 
>>>
>>
>> Why is it failing ?
>>
>> If you are under high memory pressure, then maybe if you absolutely want memory to send
>> netpoll packets, you want to grab all NAPI contexts as a way to prevent other cpus 
>> from feeding incoming packets to the host and add more memory pressure ;)
>>
> 
> I did the test with Eric's latest patch (and disable ndo_poll_controller 
> in driver). The result didn't show significant increase in drop packets. 
> I guess packet drops in my earlier test was caused by some other changes
> I mixed there. 
> 
> So I think this patch does fix the issue. Thanks Eric!

Great, this is awesome.

I will prepare a patch series for net tree.

The core infrastructure is just better at being able to drain TX completions
without risking stealing the NAPI context forever.


> 
> For ixgbe, I think we need to check napi_complete_done() return value
> anyway. Otherwise, the driver will enable IRQ in polling mode.  
> 

Sure, let's prepare such optimizations for net-next.