Re: [RFC PATCH 0/2] net: threadable napi poll loop

[Hannes Frederic Sowa]

On 11.05.2016 16:45, Eric Dumazet wrote:
> On Wed, May 11, 2016 at 7:38 AM, Paolo Abeni <pabeni@xxxxxxxxxx> wrote:
> 
>> Uh, we have likely the same issue in the net_rx_action() function, which
>> also execute with bh disabled and check for jiffies changes even on
>> single core hosts ?!?
> 
> That is why we have a loop break after netdev_budget=300 packets.
> And a sysctl to eventually tune this.
> 
> Same issue for softirq handler, look at commit
> 34376a50fb1fa095b9d0636fa41ed2e73125f214
> 
> Your questions about this central piece of networking code are worrying.
> 
>>
>> Aren't jiffies updated by the timer interrupt ? and thous even with
>> bh_disabled ?!?
> 
> Exactly my point : jiffie wont be updated in your code, since you block BH.

To be fair, jiffies get updated in hardirq and not softirq context. The
cond_resched_softirq not looking for pending softirqs is indeed a problem.

Thanks,
Hannes