CODEWITHSUNDEEP
performancelinux-kernelx86-64interruptcpu-architecture
wangt13
wangt13

Reputation: 1275

How to check IRQ latency in Linux (X86_64) for performance tuning?

Is there a way to check the interrupt processing latency in Linux kernel?

Or is there a way to check why CPU usage is only 40% in a specific configuration of Linux 4.19.138?

Background:

Currently I met a problem, I had a X86 server running either a 3rd party Linux-4.19.138 kernel (whose configuration file is about 6000 lines) or Ubuntu 20.04 X86_64 (whose configuration file is about 9500 lines long).

When running netperf test on this server , I found with the 3rd-party Linux-4.19.138 kernel, the IO latency of netperf is worse than with Ubuntu 20.04. The CPU usage is below 40% when running the 3rd party kernel, while it is about 100% when running Ubuntu 20.04.

They are using the same kernel command line and same performance profile in kernel runtime.
It seemed that the interrupt or the netserver process in the server is throttled in Linux-4.19.138.

Then, I rebuilt Ubuntu 20.04 kernel by using the short configuration file (6000 lines long), and got the similar bad results.

So it concluded that the kernel configuration made the difference.

Before comparing the 2 configurations (6000 lines vs 9500 lines), to narrow it down, my ask is, is there a way to check why CPU usage is only 40% in that configuration of 4.19.138? Or is there a way to check the interrupt processing latency in Linux kernel ?

Upvotes: 1

Views: 1066

Answers (1)

wangt13
wangt13

Reputation: 1275

I finally found the reason. It is from the
net.core.busy_read and
net.core.busy_poll are both to 0.
That means the socket polling is disabled, which impacts the netperf latency.

But the question changed to In this case, the lower CPU usage is a sign that there is something different in Linux, what kind of tool or how can we should figure out what causes the CPU usage difference in 2 kernels?

Upvotes: 1

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