Re: Select() vs Netmap

On Sunday, June 1, 2014, Fred Pedrisa <fredhps10_at_hotmail.com> wrote:

> Hey, guys.
>
>
>
>
>
> I'm currently experiencing a strange issue in my program (Using netmap).
>
>
>
> Sometimes, when I call select() in a FD, it gets like 4~8 packets per
> event,
> however suddenly it drops to 1~2 packets per event, losing a lot of
> performance and increasing the number of select calls necessary to poll the
> NIC for new packets.
>
>
>
> Is there any type of tweak I can do, to make this behavior becomes linear
> and sustain the performance in such case without these oscillations ?
>
>
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> The behavior happens under the same stressing circumstances, around 1.4
> Mpps~ (64 byte packets).


Is that one-point-four or fourteen? The firmer should be sustainable even
with short batches. In any case apart from tweaking the interrupt
 moderation parameters in the device drivers, I'd check carefully the logic
in your program and try to record a log of your activity. Average values
rarely tell the full story of what is happening.

One more thing, I think you use multuqueue, but no idea what kind of input
traffic - whether it is all for the same destination or you have a mix of
DST addresses. In the latter case, one thing to check is whether, on a
restart of the program, the driver changes the hash key in the RSS filter.
This might cause an imbalance in the traffic delivered to the queues.

Cheers
Luigi


>
>
>
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> Sincerely,
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>
>
> Fred
>
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