linux-kernel - Re: [PATCH] fix linux kernel BTF builds: increase max percpu variables by 10x

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Date: Fri, 1 Mar 2024 15:14:58 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: John Hubbard <jhubbard@...dia.com>
Cc: Alan Maguire <alan.maguire@...cle.com>, Jiri Olsa <olsajiri@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, dwarves@...r.kernel.org
Subject: Re: [PATCH] fix linux kernel BTF builds: increase max percpu
 variables by 10x

On Thu, Feb 29, 2024 at 10:15:23AM -0800, John Hubbard wrote:
> > ...
> > Running
> > 
> > bpftool btf dump file vmlinux |grep "] VAR"
> > 
> 
> $ bpftool btf dump file vmlinux |grep "] VAR" | wc -l
> 4852
> 
> $ bpftool btf dump file vmlinux |grep "] VAR" | tail -5
> [136994] VAR '_alloc_tag_cntr.9' type_id=703, linkage=static
> [137003] VAR '_alloc_tag_cntr.5' type_id=703, linkage=static
> [137004] VAR '_alloc_tag_cntr.7' type_id=703, linkage=static
> [137005] VAR '_alloc_tag_cntr.17' type_id=703, linkage=static
> [137018] VAR '_alloc_tag_cntr.14' type_id=703, linkage=static
> 
> > ...should give us a sense of what's going on. I only see 375 per-cpu
> > variables when I do this so maybe there's something
> > kernel-config-specific that might explain why you have so many more?
> 
> Yes, as mentioned earlier, this is specifically due to the .config.
> The .config is a huge distro configuration that has a lot of modules
> enabled.

could you share your .config? I tried with fedora .config and got 396
per cpu variables, I wonder where this is coming from

thanks,
jirka