From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AA335C77B7C for ; Fri, 5 May 2023 13:33:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232012AbjEENdV (ORCPT ); Fri, 5 May 2023 09:33:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56526 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231954AbjEENdU (ORCPT ); Fri, 5 May 2023 09:33:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7A2B203F2; Fri, 5 May 2023 06:33:19 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 370D36145F; Fri, 5 May 2023 13:33:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37100C433D2; Fri, 5 May 2023 13:33:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1683293598; bh=lYgIx4LtUAxSTE+FLYMqSKn8Xm5Kd/760J8cWkFOZxI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jzrZXGlhPUqc1ZlQh22FixMA6wnYqukcQ6wxPquyf+B7LZzPbxcq/0svrb0WjXFT0 UYMzCVd9a5crtktP5peVmOBMBJ0GCtYfd7ILFh4R8Xt2/gfZwbJ1Na808To+OMaJ7X EKmtLuy5EM0sFzGtSmODdaiDlNMZTTPiiKA79QRV+aBaTEB1i1PPUIkIoiLFJ07Wj5 oR0Wn7YqxOOWBg+9jRVpSn3M/QJj/j17bBinDDdUZ7IRnwpyDyrGlmp2iN4LV5jSYZ PTUevltLdI+e2qv9TKZ7+rrp4w3laRTvif7c8uzwHdPmOj6bC3GPR5HjwQeIR+q2yq F/FavQkiGYKhw== Received: by quaco.ghostprotocols.net (Postfix, from userid 1000) id ACD31403B5; Fri, 5 May 2023 10:33:15 -0300 (-03) Date: Fri, 5 May 2023 10:33:15 -0300 From: Arnaldo Carvalho de Melo To: Jiri Olsa Cc: Ian Rogers , Andrii Nakryiko , Namhyung Kim , Linus Torvalds , Song Liu , Andrii Nakryiko , Ingo Molnar , Thomas Gleixner , Clark Williams , Kate Carcia , linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, Adrian Hunter , Changbin Du , Hao Luo , James Clark , Kan Liang , Roman Lozko , Stephane Eranian , Thomas Richter , Arnaldo Carvalho de Melo , bpf Subject: Re: BPF skels in perf .Re: [GIT PULL] perf tools changes for v6.4 Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Url: http://acmel.wordpress.com Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Em Fri, May 05, 2023 at 01:03:14AM +0200, Jiri Olsa escreveu: > On Thu, May 04, 2023 at 03:03:42PM -0700, Ian Rogers wrote: > > On Thu, May 4, 2023 at 2:48 PM Arnaldo Carvalho de Melo wrote: > > > > > > Em Thu, May 04, 2023 at 04:07:29PM -0300, Arnaldo Carvalho de Melo escreveu: > > > > Em Thu, May 04, 2023 at 11:50:07AM -0700, Andrii Nakryiko escreveu: > > > > > On Thu, May 4, 2023 at 10:52 AM Arnaldo Carvalho de Melo wrote: > > > > > > Andrii, can you add some more information about the usage of vmlinux.h > > > > > > instead of using kernel headers? > > > > > > > > > I'll just say that vmlinux.h is not a hard requirement to build BPF > > > > > programs, it's more a convenience allowing easy access to definitions > > > > > of both UAPI and kernel-internal structures for tracing needs and > > > > > marking them relocatable using BPF CO-RE machinery. Lots of real-world > > > > > applications just check-in pregenerated vmlinux.h to avoid build-time > > > > > dependency on up-to-date host kernel and such. > > > > > > > > > If vmlinux.h generation and usage is causing issues, though, given > > > > > that perf's BPF programs don't seem to be using many different kernel > > > > > types, it might be a better option to just use UAPI headers for public > > > > > kernel type definitions, and just define CO-RE-relocatable minimal > > > > > definitions locally in perf's BPF code for the other types necessary. > > > > > E.g., if perf needs only pid and tgid from task_struct, this would > > > > > suffice: > > > > > > > > > struct task_struct { > > > > > int pid; > > > > > int tgid; > > > > > } __attribute__((preserve_access_index)); > > > > > > > > Yeah, that seems like a way better approach, no vmlinux involved, libbpf > > > > CO-RE notices that task_struct changed from this two integers version > > > > (of course) and does the relocation to where it is in the running kernel > > > > by using /sys/kernel/btf/vmlinux. > > > > > > Doing it for one of the skels, build tested, runtime untested, but not > > > using any vmlinux, BTF to help, not that bad, more verbose, but at least > > > we state what are the fields we actually use, have those attribute > > > documenting that those offsets will be recorded for future use, etc. > > > > > > Namhyung, can you please check that this works? > > > > > > Thanks, > > > > > > - Arnaldo > > > > > > diff --git a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > > index 6a438e0102c5a2cb..f376d162549ebd74 100644 > > > --- a/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > > +++ b/tools/perf/util/bpf_skel/bperf_cgroup.bpf.c > > > @@ -1,11 +1,40 @@ > > > // SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > > > // Copyright (c) 2021 Facebook > > > // Copyright (c) 2021 Google > > > -#include "vmlinux.h" > > > +#include > > > +#include > > > > Compared to vmlinux.h here be dragons. It is easy to start dragging in > > all of libc and that may not work due to missing #ifdefs, etc.. Could > > we check in a vmlinux.h like libbpf-tools does? > > https://github.com/iovisor/bcc/tree/master/libbpf-tools#vmlinuxh-generation > > https://github.com/iovisor/bcc/tree/master/libbpf-tools/arm64 > > > > This would also remove some of the errors that could be introduced by > > copy+pasting enums, etc. and also highlight issues with things being > > renamed as build time rather than runtime failures. > > we already have to deal with that, right? doing checks on fields in > structs like mm_struct___old > > > Could this be some shared resource for the different linux tools > > projects using a vmlinux.h? e.g. tools/lib/vmlinuxh with an > > install_headers target that builds a vmlinux.h. > > I tried to do the minimal header and it's not too big, > I pushed it in here: > https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/log/?h=perf/vmlinux_h > > compile tested so far I see it and it makes the change to be minimal, which is good at the current stage, but I wonder if it wouldn't be better for us to define just the ones not in UAPI and use the #include , as I did in the patches I posted here and Namhyung tested at least one, this way the added vmlinux.h file get even smaller by not including things like: [acme@quaco perf-tools]$ egrep -w '(perf_event_sample_format|bpf_perf_event_value|perf_sample_weight|perf_mem_data_src) {' include/uapi/linux/*.h include/uapi/linux/bpf.h:struct bpf_perf_event_value { include/uapi/linux/perf_event.h:enum perf_event_sample_format { include/uapi/linux/perf_event.h:union perf_mem_data_src { include/uapi/linux/perf_event.h:union perf_mem_data_src { include/uapi/linux/perf_event.h:union perf_sample_weight { [acme@quaco perf-tools]$ Also why do we need these: +struct mm_struct { +} __attribute__((preserve_access_index)); + +struct raw_spinlock { +} __attribute__((preserve_access_index)); + +typedef struct raw_spinlock raw_spinlock_t; + +struct spinlock { +} __attribute__((preserve_access_index)); + +typedef struct spinlock spinlock_t; + +struct sighand_struct { + spinlock_t siglock; +} __attribute__((preserve_access_index)); We don't use them, they're just pointers you kept on: +struct task_struct { + struct css_set *cgroups; + pid_t pid; + pid_t tgid; + char comm[16]; + struct mm_struct *mm; + struct sighand_struct *sighand; + unsigned int flags; +} __attribute__((preserve_access_index)); That with the preserve_access_index isn't needed, we need just the fields that we access in the tools, right? - Arnaldo