Re: big picture UDP/IP performance question re 2.6.18 -> 2.6.32

From: starlight
Date: Wed Oct 05 2011 - 07:58:54 EST

At 10:53 AM 10/5/2011 +0200, Eric Dumazet wrote:
>Note :
>Your results are from a combination of a user
>application and kernel default strategies.
>On other combinations, results can be completely different.
>A wakeup strategy is somewhat tricky :
>- Should we affine or not.
>- Should we queue the wakeup on a remote CPU,
> to keep scheduler data hot in a single cpu cache.
>- Should we use RPS/RFS to queue the packet to
> another CPU before even handling it in our stack,
> to keep network data hot in a single cpu
> cache. (check Documentation/networking/scaling.txt)
>At least, with recent kernels, we have many
>available choices to tune a workload.

I would argue that results speak louder than
features. A 300% deterioration in latency,
600% deterioration in sigma latency and
a 50-100% increase in apparent system overhead
is not impressive.

Our application is designed to run optimally
as a scalable real-time network transaction
processor and provides for a variety of
different thread-pool and queuing approaches.
Performance is worse for every one of them
in newer kernels. The ones that scale the
best fared worst.

It seems to me that any scheduler-intensive
application will suffer a similar fate.

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