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 EDA63C433FE for ; Tue, 1 Nov 2022 20:04:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229926AbiKAUE0 (ORCPT ); Tue, 1 Nov 2022 16:04:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbiKAUEY (ORCPT ); Tue, 1 Nov 2022 16:04:24 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 750201C437; Tue, 1 Nov 2022 13:04:23 -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 E93A96171A; Tue, 1 Nov 2022 20:04:22 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4A1A2C4347C; Tue, 1 Nov 2022 20:04:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1667333062; bh=7XHcT9f5J4g8DUVSlnwzPNm8LhYkpUS0/AMNBo9GJUw=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=FBRvkOYHviuunbD60ryqT2SJpVXzILmLsbk4oCCN1PPUfZRoRMXfcftBWHsnhzQvP X2rSulY8YSkIZTb1mdOW9/BA3EwawUJp3PVXrugJeQMkBARSHfXu4/9KvsFeAqQm8b l2sWys+IS01a7pFM36ouHY/NolCKq1SFzVWSL8Z0Z7BoX7awZgJE6hXdVDD0qcy5SK fsHusHEjEAJgmJey+F5Rhiy6pdb3Ss9ZJF4fbgHu8BGyIjt8DubYtOaJOd4c0yYpIl yBzPGVjBPguUyB9EhYyaE92t3RNK8lJrwAdUVkFgozFeI+NgOlGqzcdN+gQtN1SCh7 bV9Y0/tHfzlhw== Received: by mail-ej1-f44.google.com with SMTP id y14so39864568ejd.9; Tue, 01 Nov 2022 13:04:22 -0700 (PDT) X-Gm-Message-State: ACrzQf0F5hkJS42QDJN3kX7JcBbpT9JvcrrLh0QVtpOL76gV/6jaVgdw V6ZJSf5IUCKvDAopbQqIYNliDQcRV2HVSmvgT6s= X-Google-Smtp-Source: AMsMyM4BvokXG3mZAS3b6jtYCaK0TRjw2+YB+yV5CbP3BvAOvmHfYrXMyuLHe6QIfsRHg3bjK47x7pBeER/rI4lAZaE= X-Received: by 2002:a17:906:eec1:b0:782:6384:76be with SMTP id wu1-20020a170906eec100b00782638476bemr19830640ejb.756.1667333060421; Tue, 01 Nov 2022 13:04:20 -0700 (PDT) MIME-Version: 1.0 References: <20221101052340.1210239-1-namhyung@kernel.org> <20221101052340.1210239-3-namhyung@kernel.org> In-Reply-To: From: Song Liu Date: Tue, 1 Nov 2022 13:04:08 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH bpf-next 2/3] bpf: Add bpf_perf_event_read_sample() helper To: Alexei Starovoitov Cc: Jiri Olsa , Namhyung Kim , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Song Liu , Peter Zijlstra , Martin KaFai Lau , Yonghong Song , John Fastabend , KP Singh , Hao Luo , Stanislav Fomichev , LKML , bpf , Steven Rostedt , Ingo Molnar , Arnaldo Carvalho de Melo Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 1, 2022 at 11:53 AM Alexei Starovoitov wrote: > > On Tue, Nov 1, 2022 at 11:47 AM Song Liu wrote: > > > > On Tue, Nov 1, 2022 at 11:26 AM Alexei Starovoitov > > wrote: > > > > > > On Tue, Nov 1, 2022 at 3:03 AM Jiri Olsa wrote: > > > > > > > > On Mon, Oct 31, 2022 at 10:23:39PM -0700, Namhyung Kim wrote: > > > > > The bpf_perf_event_read_sample() helper is to get the specified sample > > > > > data (by using PERF_SAMPLE_* flag in the argument) from BPF to make a > > > > > decision for filtering on samples. Currently PERF_SAMPLE_IP and > > > > > PERF_SAMPLE_DATA flags are supported only. > > > > > > > > > > Signed-off-by: Namhyung Kim > > > > > --- > > > > > include/uapi/linux/bpf.h | 23 ++++++++++++++++ > > > > > kernel/trace/bpf_trace.c | 49 ++++++++++++++++++++++++++++++++++ > > > > > tools/include/uapi/linux/bpf.h | 23 ++++++++++++++++ > > > > > 3 files changed, 95 insertions(+) > > > > > > > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > > > > index 94659f6b3395..cba501de9373 100644 > > > > > --- a/include/uapi/linux/bpf.h > > > > > +++ b/include/uapi/linux/bpf.h > > > > > @@ -5481,6 +5481,28 @@ union bpf_attr { > > > > > * 0 on success. > > > > > * > > > > > * **-ENOENT** if the bpf_local_storage cannot be found. > > > > > + * > > > > > + * long bpf_perf_event_read_sample(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 sample_flags) > > > > > + * Description > > > > > + * For an eBPF program attached to a perf event, retrieve the > > > > > + * sample data associated to *ctx* and store it in the buffer > > > > > + * pointed by *buf* up to size *size* bytes. > > > > > + * > > > > > + * The *sample_flags* should contain a single value in the > > > > > + * **enum perf_event_sample_format**. > > > > > + * Return > > > > > + * On success, number of bytes written to *buf*. On error, a > > > > > + * negative value. > > > > > + * > > > > > + * The *buf* can be set to **NULL** to return the number of bytes > > > > > + * required to store the requested sample data. > > > > > + * > > > > > + * **-EINVAL** if *sample_flags* is not a PERF_SAMPLE_* flag. > > > > > + * > > > > > + * **-ENOENT** if the associated perf event doesn't have the data. > > > > > + * > > > > > + * **-ENOSYS** if system doesn't support the sample data to be > > > > > + * retrieved. > > > > > */ > > > > > #define ___BPF_FUNC_MAPPER(FN, ctx...) \ > > > > > FN(unspec, 0, ##ctx) \ > > > > > @@ -5695,6 +5717,7 @@ union bpf_attr { > > > > > FN(user_ringbuf_drain, 209, ##ctx) \ > > > > > FN(cgrp_storage_get, 210, ##ctx) \ > > > > > FN(cgrp_storage_delete, 211, ##ctx) \ > > > > > + FN(perf_event_read_sample, 212, ##ctx) \ > > > > > /* */ > > > > > > > > > > /* backwards-compatibility macros for users of __BPF_FUNC_MAPPER that don't > > > > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > > > > > index ce0228c72a93..befd937afa3c 100644 > > > > > --- a/kernel/trace/bpf_trace.c > > > > > +++ b/kernel/trace/bpf_trace.c > > > > > @@ -28,6 +28,7 @@ > > > > > > > > > > #include > > > > > #include > > > > > +#include > > > > > > > > > > #include > > > > > > > > > > @@ -1743,6 +1744,52 @@ static const struct bpf_func_proto bpf_read_branch_records_proto = { > > > > > .arg4_type = ARG_ANYTHING, > > > > > }; > > > > > > > > > > +BPF_CALL_4(bpf_perf_event_read_sample, struct bpf_perf_event_data_kern *, ctx, > > > > > + void *, buf, u32, size, u64, flags) > > > > > +{ > > > > > > > > I wonder we could add perf_btf (like we have tp_btf) program type that > > > > could access ctx->data directly without helpers > > > > > > > > > + struct perf_sample_data *sd = ctx->data; > > > > > + void *data; > > > > > + u32 to_copy = sizeof(u64); > > > > > + > > > > > + /* only allow a single sample flag */ > > > > > + if (!is_power_of_2(flags)) > > > > > + return -EINVAL; > > > > > + > > > > > + /* support reading only already populated info */ > > > > > + if (flags & ~sd->sample_flags) > > > > > + return -ENOENT; > > > > > + > > > > > + switch (flags) { > > > > > + case PERF_SAMPLE_IP: > > > > > + data = &sd->ip; > > > > > + break; > > > > > + case PERF_SAMPLE_ADDR: > > > > > + data = &sd->addr; > > > > > + break; > > > > > > > > AFAICS from pe_prog_convert_ctx_access you should be able to read addr > > > > directly from context right? same as sample_period.. so I think if this > > > > will be generic way to read sample data, should we add sample_period > > > > as well? > > > > > > +1 > > > Let's avoid new stable helpers for this. > > > Pls use CORE and read perf_sample_data directly. > > > > We have legacy ways to access sample_period and addr with > > struct bpf_perf_event_data and struct bpf_perf_event_data_kern. I > > think mixing that > > with CORE makes it confusing for the user. And a helper or a kfunc would make it > > easier to follow. perf_btf might also be a good approach for this. > > imo that's a counter argument to non-CORE style. > struct bpf_perf_event_data has sample_period and addr, > and as soon as we pushed the boundaries it turned out it's not enough. > Now we're proposing to extend uapi a bit with sample_ip. > That will repeat the same mistake. > Just use CORE and read everything that is there today > and will be there in the future. Another work of this effort is that we need the perf_event to prepare required fields before calling the BPF program. I think we will need some logic in addition to CORE to get that right. How about we add perf_btf where the perf_event prepare all fields before calling the BPF program? perf_btf + CORE will be able to read all fields in the sample. Thanks, Song