netdev - Re: [PATCH bpf-next v2 1/5] bpf: make MAX_BPF_FUNC

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Date: Fri, 2 Jun 2023 11:17:29 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Menglong Dong <menglong8.dong@...il.com>
Cc: Jiri Olsa <olsajiri@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, 
	John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, 
	"H. Peter Anvin" <hpa@...or.com>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>, 
	benbjiang@...cent.com, Ilya Leoshkevich <iii@...ux.ibm.com>, 
	Menglong Dong <imagedong@...cent.com>, Xu Kuohai <xukuohai@...wei.com>, 
	Manu Bretelle <chantr4@...il.com>, Ross Zwisler <zwisler@...gle.com>, Eddy Z <eddyz87@...il.com>, 
	Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 1/5] bpf: make MAX_BPF_FUNC_ARGS 14

On Fri, Jun 2, 2023 at 12:01 AM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> According to the current kernel version, below is a statistics of the
> function arguments count:
>
> argument count | FUNC_PROTO count
> 7              | 367
> 8              | 196
> 9              | 71
> 10             | 43
> 11             | 22
> 12             | 10
> 13             | 15
> 14             | 4
> 15             | 0
> 16             | 1
>
> It's hard to statisics the function count, so I use FUNC_PROTO in the btf
> of vmlinux instead. The function with 16 arguments is ZSTD_buildCTable(),
> which I think can be ignored.
>
> Therefore, let's make the maximum of function arguments count 14. It used
> to be 12, but it seems that there is no harm to make it big enough.

I think we're just fine at 12.
People need to fix their code. ZSTD_buildCTable should be first in line.
Passing arguments on the stack is not efficient from performance pov.