From mboxrd@z Thu Jan 1 00:00:00 1970 From: Song Liu Subject: Re: [RFC perf,bpf 1/5] perf, bpf: Introduce PERF_RECORD_BPF_EVENT Date: Wed, 7 Nov 2018 18:25:04 +0000 Message-ID: <31067290-4B66-4AA1-8027-607397BC0264@fb.com> References: <20181106205246.567448-1-songliubraving@fb.com> <20181106205246.567448-2-songliubraving@fb.com> <20181107084057.GG9781@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Cc: Netdev , lkml , Kernel Team , "ast@kernel.org" , "daniel@iogearbox.net" , "acme@kernel.org" To: Peter Zijlstra Return-path: In-Reply-To: <20181107084057.GG9781@hirez.programming.kicks-ass.net> Content-Language: en-US Content-ID: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org > On Nov 7, 2018, at 12:40 AM, Peter Zijlstra wrote: >=20 > On Tue, Nov 06, 2018 at 12:52:42PM -0800, Song Liu wrote: >> For better performance analysis of BPF programs, this patch introduces >> PERF_RECORD_BPF_EVENT, a new perf_event_type that exposes BPF program >> load/unload information to user space. >>=20 >> /* >> * Record different types of bpf events: >> * enum perf_bpf_event_type { >> * PERF_BPF_EVENT_UNKNOWN =3D 0, >> * PERF_BPF_EVENT_PROG_LOAD =3D 1, >> * PERF_BPF_EVENT_PROG_UNLOAD =3D 2, >> * }; >> * >> * struct { >> * struct perf_event_header header; >> * u16 type; >> * u16 flags; >> * u32 id; // prog_id or map_id >> * }; >> */ >> PERF_RECORD_BPF_EVENT =3D 17, >>=20 >> PERF_RECORD_BPF_EVENT contains minimal information about the BPF program= . >> Perf utility (or other user space tools) should listen to this event and >> fetch more details about the event via BPF syscalls >> (BPF_PROG_GET_FD_BY_ID, BPF_OBJ_GET_INFO_BY_FD, etc.). >=20 > Why !? You're failing to explain why it cannot provide the full > information there. Aha, I missed this part. I will add the following to next version. Please let me know if anything is not clear. Thanks, Song This design decision is picked for the following reasons. First, BPF=20 programs could be loaded-and-jited and/or unloaded before/during/after=20 perf-record run. Once a BPF programs is unloaded, it is impossible to=20 recover details of the program. It is impossible to provide the=20 information through a simple key (like the build ID). Second, BPF prog annotation is under fast developments. Multiple informations will be=20 added to bpf_prog_info in the next few releases. Including all the information of a BPF program in the perf ring buffer requires frequent=20 changes to the perf ABI, and thus makes it very difficult to manage=20 compatibility of perf utility.=20 For more information on this topic, please refer to the following=20 discussions:=20 https://www.spinics.net/lists/netdev/msg524230.html