[PATCH] procfs: add syscall statistics

[Alexei Starovoitov]

On Fri, May 27, 2022 at 4:10 AM Zhang Yuchen
<zhangyuchen.lcr at bytedance.com> wrote:
>
> Add /proc/syscalls to display percpu syscall count.

I second Peter's nack.
We don't add debug features to the production kernel.

> We need a less resource-intensive way to count syscall per cpu
> for system problem location.
>
> There is a similar utility syscount in the BCC project, but syscount
> has a high performance cost.

There are two syscount tools in BCC:
tools/syscount
libbpf-tools/syscount

Which one has this 42% overhead?

The former tool is obsolete though.
It was written in the days when bpf had 1/10 of
the features it has today.
Both tools can be optimized.
They attach to raw_syscalls tracepoint.
tracepoints are not cheap.
In terms of overhead:
tracepoint > raw_tracepoint > fentry.
bpf can attach to all three.

Please profile libbpf-tools/syscount tool
with perf and unixbench, understand where overhead
comes from and then optimize the tool.