Re: [PATCH bpf] libbpf: skip base btf sanity checks

[Alan Maguire <alan.maguire@oracle.com>]

On 24/06/2024 10:09, Antoine Tenart wrote:
> When upgrading to libbpf 1.3 we noticed a big performance hit while
> loading programs using CORE on non base-BTF symbols. This was tracked
> down to the new BTF sanity check logic. The issue is the base BTF
> definitions are checked first for the base BTF and then again for every
> module BTF.
> 
> Loading 5 dummy programs (using libbpf-rs) that are using CORE on a
> non-base BTF symbol on my system:
> - Before this fix: 3s.
> - With this fix: 0.1s.
> 
> Fix this by only checking the types starting at the BTF start id. This
> should ensure the base BTF is still checked as expected but only once
> (btf->start_id == 1 when creating the base BTF), and then only
> additional types are checked for each module BTF.
> 
> Fixes: 3903802bb99a ("libbpf: Add basic BTF sanity validation")
> Signed-off-by: Antoine Tenart <atenart@kernel.org>

This looks good to me.

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>

> ---
>  tools/lib/bpf/btf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
> index 2d0840ef599a..142060bbce0a 100644
> --- a/tools/lib/bpf/btf.c
> +++ b/tools/lib/bpf/btf.c
> @@ -598,7 +598,7 @@ static int btf_sanity_check(const struct btf *btf)
>  	__u32 i, n = btf__type_cnt(btf);
>  	int err;
>  
> -	for (i = 1; i < n; i++) {
> +	for (i = btf->start_id; i < n; i++) {
>  		t = btf_type_by_id(btf, i);
>  		err = btf_validate_type(btf, t, i);
>  		if (err)