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 X-Spam-Level: X-Spam-Status: No, score=-6.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 003EBC433DF for ; Tue, 26 May 2020 17:40:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C89D720776 for ; Tue, 26 May 2020 17:40:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="rS2CV3OK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388900AbgEZRkg (ORCPT ); Tue, 26 May 2020 13:40:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48364 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388061AbgEZRkf (ORCPT ); Tue, 26 May 2020 13:40:35 -0400 Received: from mail-qv1-xf43.google.com (mail-qv1-xf43.google.com [IPv6:2607:f8b0:4864:20::f43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B5064C03E96D; Tue, 26 May 2020 10:40:35 -0700 (PDT) Received: by mail-qv1-xf43.google.com with SMTP id l3so9842542qvo.7; Tue, 26 May 2020 10:40:35 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=Qb+yBWRLKYxH7UqNrksjpc0mUvlYqjaZssX2PBNYDD8=; b=rS2CV3OKs95vc6mBre1VvOg0yINpVuR2K+Vr3/o8BSW/WAw0vZizsBtzA2KX0wtyD4 qxNBeo+eNcZHZLev0sVZBhD06B4UhKFlhEaGFCfdnq6lsrAcRlfdhA1yO+7oStfJYTfF 5cvVpYG/Xi4KpXfoeT5Is9/O0cpDrRPIJ69k+dkMioQddm++XGIvWGjo1AJPVgRHmxvJ 009ECegQ5chyPuSSGdLGr+p1JWYe4BnOwk0X6XiLabLgR3l2jUmspX8d/hmE2wctqGX1 t2WthMdSz8alKXdoWU8vPW76qdY+ueJRxJubPIW4mAQsTGvw1ClYV04fScF+LeUmstiB k2hQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=Qb+yBWRLKYxH7UqNrksjpc0mUvlYqjaZssX2PBNYDD8=; b=EjmqJY0oklrBDhkuYLgUai6b6Kcw+w6v3+tAZcTB/2NvCSZC9svYEpFIErNgUf7HB3 JjHL10PqoA1e2A4I95h8NpW2AkOrydqEOIDt5+Orz7tUiRv0hb4EU2UPzdlUlh3ZsIWG fA8/nILiSwTn60bMb5+VdmjDqDAnlM2MKt5Xh52KQRhpFekr8X/VROEf50ApXUdZXIjJ mqCnumSLXmj2EtQatI3cP2Zc1u5GCv0t6PCvTjiGGTZfu6WQU+xhKuQJYNBM/HngkuES TRXDPqJcqhtgYk4d3MeC0laBOv9GxxP7NmeLpR0kGYatX9xAsU9VlERQDX782X11hUNL u/iw== X-Gm-Message-State: AOAM530PbHAMXpdNuBdVetnAHqFnN1q4ktMNrFKsYzmvIxnj6ZDZ2JJt 0qWWfRv9aHS+YfWFxTs8dq3FqbZp0KzZLJcUkpIAS2CE6eB3sQ== X-Google-Smtp-Source: ABdhPJx66BcJwXQyt+0F15+M/l3RHSkuq2b2r6veZfnixsWv0/r7en8Tvgl9PIHhSKw//ZskGURLSQyIHBM9NSs6BW8= X-Received: by 2002:a0c:b92f:: with SMTP id u47mr7719557qvf.247.1590514834628; Tue, 26 May 2020 10:40:34 -0700 (PDT) MIME-Version: 1.0 References: <159042332675.79900.6845937535091126683.stgit@ebuild> <51FAF2C0-F843-45EF-8CE7-69FD0334AD84@redhat.com> In-Reply-To: <51FAF2C0-F843-45EF-8CE7-69FD0334AD84@redhat.com> From: Andrii Nakryiko Date: Tue, 26 May 2020 10:40:23 -0700 Message-ID: Subject: Re: [PATCH bpf-next] libbpf: add API to consume the perf ring buffer content To: Eelco Chaudron Cc: bpf , "David S. Miller" , Networking , Alexei Starovoitov , Daniel Borkmann , Martin Lau , Song Liu , Yonghong Song , Andrii Nakryiko , =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, May 26, 2020 at 1:07 AM Eelco Chaudron wrote: > > > > On 26 May 2020, at 7:29, Andrii Nakryiko wrote: > > > On Mon, May 25, 2020 at 2:01 PM Eelco Chaudron > > wrote: > >> > >> This new API, perf_buffer__consume, can be used as follows: > > > > I wonder, was it inspired by yet-to-be committed > > ring_buffer__consume() or it's just a coincidence? > > Just coincidence, I was needing a function to flush the remaining ring > entries, as I was using a larger wakeup_events value. > Initially, I called the function ring_buffer_flush(), but once I noticed > your patch I renamed it :) Nice, thanks, I love consistent naming :) > > >> - When you have a perf ring where wakeup_events is higher than 1, > >> and you have remaining data in the rings you would like to pull > >> out on exit (or maybe based on a timeout). > >> - For low latency cases where you burn a CPU that constantly polls > >> the queues. > >> > >> Signed-off-by: Eelco Chaudron > >> --- > >> tools/lib/bpf/libbpf.c | 23 +++++++++++++++++++++++ > >> tools/lib/bpf/libbpf.h | 1 + > >> tools/lib/bpf/libbpf.map | 1 + > >> 3 files changed, 25 insertions(+) > >> > >> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > >> index fa04cbe547ed..cbef3dac7507 100644 > >> --- a/tools/lib/bpf/libbpf.c > >> +++ b/tools/lib/bpf/libbpf.c > >> @@ -8456,6 +8456,29 @@ int perf_buffer__poll(struct perf_buffer *pb, > >> int timeout_ms) > >> return cnt < 0 ? -errno : cnt; > >> } > >> > >> +int perf_buffer__consume(struct perf_buffer *pb) > >> +{ > >> + int i; > >> + > >> + if (!pb) > >> + return -EINVAL; > > > > we don't check this in perf_buffer__poll, IMO, checking this in every > > "method" is an overkill. > > Ack, will fix in v2 > > >> + > >> + if (!pb->cpu_bufs) > >> + return 0; > > > > no need to check. It's either non-NULL for valid perf_buffer, or > > calloc could return NULL if pb->cpu_cnt is zero (not sure it's > > possible, but still), but then loop below will never access > > pb->cpu_bufs[i]. > > Agreed, was just adding some safety checks, but in the constantly poll > mode this is a lot of overhead. Will remover in v2. > > >> + > >> + for (i =3D 0; i < pb->cpu_cnt && pb->cpu_bufs[i]; i++) { > > > > I think pb->cpu_bufs[i] check is wrong, it will stop iteration > > prematurely if cpu_bufs are sparsely populated. So move check inside > > and continue loop if NULL. > > Mimicked the behavior from other functions, however just to be safe I > split it up. You mean perf_buffer__poll() or perf_buffer__free() loop? In the perf_buffer__poll() case, first N events will always correspond to non-NULL buffers. It's very different from what you are doing here. But I think perf_buffer__free() actually is buggy similarly to how I pointed out in this case. We need to fix that. > > >> + int err; > > > > nit: declare it together with "i" above, similar to how > > perf_buffer__poll does it > > Put it down here as it=E2=80=99s only used in the context of the for loop= , but > will move it up in the v2. > > >> + struct perf_cpu_buf *cpu_buf =3D pb->cpu_bufs[i]; > >> + > >> + err =3D perf_buffer__process_records(pb, cpu_buf); > >> + if (err) { > >> + pr_warn("error while processing records: > >> %d\n", err); > >> + return err; > >> + } > >> + } > >> + return 0; > >> +} > >> + > >> struct bpf_prog_info_array_desc { > >> int array_offset; /* e.g. offset of jited_prog_insns */ > >> int count_offset; /* e.g. offset of jited_prog_len */ > >> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h > >> index 8ea69558f0a8..1e2e399a5f2c 100644 > >> --- a/tools/lib/bpf/libbpf.h > >> +++ b/tools/lib/bpf/libbpf.h > >> @@ -533,6 +533,7 @@ perf_buffer__new_raw(int map_fd, size_t page_cnt, > >> > >> LIBBPF_API void perf_buffer__free(struct perf_buffer *pb); > >> LIBBPF_API int perf_buffer__poll(struct perf_buffer *pb, int > >> timeout_ms); > >> +LIBBPF_API int perf_buffer__consume(struct perf_buffer *pb); > >> > >> typedef enum bpf_perf_event_ret > >> (*bpf_perf_event_print_t)(struct perf_event_header *hdr, > >> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map > >> index 0133d469d30b..381a7342ecfc 100644 > >> --- a/tools/lib/bpf/libbpf.map > >> +++ b/tools/lib/bpf/libbpf.map > >> @@ -262,4 +262,5 @@ LIBBPF_0.0.9 { > >> bpf_link_get_fd_by_id; > >> bpf_link_get_next_id; > >> bpf_program__attach_iter; > >> + perf_buffer__consume; > >> } LIBBPF_0.0.8; > >> > > Thanks for the review, will send out a v2 soon. >