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From Leif Hedstrom <>
Subject Re: ksoftirqd and traffic server load testing
Date Tue, 28 Jul 2015 00:09:07 GMT

> On Jul 24, 2015, at 9:15 AM, Steve Malenfant <> wrote:
> During HLS load testing, I'm seeing high ksoftirqd usage (99%) and traffic starts to
slow down. Load on traffic server seems OK.
> Has anybody noticed that before and is there an irqbalance/numa change that needs to
be used by ixgbe adapter to work around it?
>    PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND               
>      9 root      20   0     0    0    0 R 98.0  0.0  26:07.07 ksoftirqd/1  

There’s not a whole lot you can do on the ATS side of things. You can fiddle with the NUMA
/ CPU affinity settings, and perhaps disable accept threads as well (that allows the conn
to be accepted and processed on a single net-thread).

Now, I know for a fact that Linux is notoriously annoying when it comes to SIRQs. Our team
at work spent a significant amount of time figuring out how to balance the IRQs best. I’ll
see if maybe John or Ask can contribute something here, explaining all the magic they had
to do. Ask / John, either of you reading this? :-).

— leif

CONFIG proxy.config.accept_threads INT 0
CONFIG proxy.config.exec_thread.affinity INT 1

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