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Mon, 27 Oct 2025 12:06:33 -0700 (PDT) Received: from [192.168.0.226] ([38.34.87.7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-33fed81ca93sm9366998a91.19.2025.10.27.12.06.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Oct 2025 12:06:33 -0700 (PDT) Message-ID: <6e7ef94cb4e2d7fbc82676b2af1a165cac620aae.camel@gmail.com> Subject: Re: [RFC PATCH v3 1/3] btf: implement BTF type sorting for accelerated lookups From: Eduard Zingerman To: Donglin Peng , ast@kernel.org, Andrii Nakryiko Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Alan Maguire , Song Liu , pengdonglin Date: Mon, 27 Oct 2025 12:06:30 -0700 In-Reply-To: <20251027135423.3098490-2-dolinux.peng@gmail.com> References: <20251027135423.3098490-1-dolinux.peng@gmail.com> <20251027135423.3098490-2-dolinux.peng@gmail.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-10-27 at 21:54 +0800, Donglin Peng wrote: [...] Question to Andrii, I think. It looks a bit asymmetrical, that there is btf_check_sorted() in libbpf, but library does not provide comparison or sorting function. Wdyt? > +static void btf_check_sorted(struct btf *btf, int start_id) > +{ > + const struct btf_type *t; > + int i, n, nr_sorted_types; > + > + n =3D btf__type_cnt(btf); > + if (btf->nr_types < BTF_CHECK_SORT_THRESHOLD) > + return; > + > + n--; > + nr_sorted_types =3D 0; > + for (i =3D start_id; i < n; i++) { > + int k =3D i + 1; > + > + if (btf_compare_type_kinds_names(&i, &k, btf) > 0) > + return; > + > + t =3D btf_type_by_id(btf, k); > + if (!str_is_empty(btf__str_by_offset(btf, t->name_off))) > + nr_sorted_types++; > + } > + > + t =3D btf_type_by_id(btf, start_id); > + if (!str_is_empty(btf__str_by_offset(btf, t->name_off))) > + nr_sorted_types++; > + > + if (nr_sorted_types < BTF_CHECK_SORT_THRESHOLD) > + return; Nit: Still think that this is not needed. It trades a couple of CPU cycles for this check and a big comment on the top, about why it's needed. > + > + btf->nr_sorted_types =3D nr_sorted_types; > +} [...]