Preventing ng_callout() timeouts to trigger packet queuing

[Karim Fodil-Lemelin]

Hi,

By the way this change has opened the gates to greater performance for 
us when using ng_callout() inside nodes. In some cases we see twice as 
much pps since packets are direct dispatched instead of being queued in 
software interrupts threads (swi*).

Thanks,

Karim

PS: I did file a PR : kern/188421

On 09/04/2014 9:09 PM, Adrian Chadd wrote:
> Hi!
>
> Would you mind filing a PR for this?
>
> www.freebsd.org/send-pr.html
>
> That way it won't (hopefully!) get lost.
>
> Thanks!
>
>
> -a
>
>
> On 9 April 2014 14:25, Karim Fodil-Lemelin <fodillemlinkarim at gmail.com> wrote:
>> Hi,
>>
>> Below is a revised patch for this issue. It accounts for nodes or hooks that
>> explicitly need to be queuing:
>>
>> @@ -3632,7 +3632,12 @@ ng_callout(struct callout *c, node_p node, hook_p
>> hook, int ticks,
>>
>>          if ((item = ng_alloc_item(NGQF_FN, NG_NOFLAGS)) == NULL)
>>                  return (ENOMEM);
>>
>> -       item->el_flags |= NGQF_WRITER;
>> +       if ((node->nd_flags & NGF_FORCE_WRITER) ||
>> +           (hook && (hook->hk_flags & HK_FORCE_WRITER)))
>>
>> +         item->el_flags |= NGQF_WRITER;
>> +       else
>>
>> +         item->el_flags |= NGQF_READER;
>> +
>>          NG_NODE_REF(node);              /* and one for the item */
>>          NGI_SET_NODE(item, node);
>>          if (hook) {
>>
>> Regards,
>>
>> Karim.
>>
>>
>> On 09/04/2014 3:16 PM, Karim Fodil-Lemelin wrote:
>>> Hi List,
>>>
>>> I'm calling out to the general wisdom ... I have seen an issue in netgraph
>>> where, if called, a callout routine registered by ng_callout() will trigger
>>> packet queuing inside the worklist of netgraph since ng_callout() makes my
>>> node suddenly a WRITER node (therefore non reentrant) for the duration of
>>> the call.
>>>
>>> So as soon as the callout function returns, all following packets will get
>>> directly passed to the node again and when the ngintr thread gets executed
>>> then only then will I get the queued packets. This introduces out of order
>>> packets in the flow. I am using the current patch below to solve the issue
>>> and I am wondering if there is anything wrong with it (and maybe contribute
>>> back :):
>>>
>>>
>>> @@ -3632,7 +3632,7 @@ ng_callout(struct callout *c, node_p node, hook_p
>>> hook, int ticks,
>>>          if ((item = ng_alloc_item(NGQF_FN, NG_NOFLAGS)) == NULL)
>>>                  return (ENOMEM);
>>>
>>> -       item->el_flags |= NGQF_WRITER;
>>> +       item->el_flags = NGQF_READER;
>>>          NG_NODE_REF(node);              /* and one for the item */
>>>          NGI_SET_NODE(item, node);
>>>          if (hook) {
>>>
>>>
>>> Best regards,
>>>
>>> Karim.
>>> _______________________________________________
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>>
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