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=-4.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 52F6BC433E0 for ; Wed, 5 Aug 2020 17:55:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2106B21D95 for ; Wed, 5 Aug 2020 17:55:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="tT0P2gfI" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728472AbgHERzn (ORCPT ); Wed, 5 Aug 2020 13:55:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729062AbgHERzO (ORCPT ); Wed, 5 Aug 2020 13:55:14 -0400 Received: from mail-pg1-x543.google.com (mail-pg1-x543.google.com [IPv6:2607:f8b0:4864:20::543]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B0875C06179E; Wed, 5 Aug 2020 10:45:57 -0700 (PDT) Received: by mail-pg1-x543.google.com with SMTP id t6so24880229pgq.1; Wed, 05 Aug 2020 10:45:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=HFuNCX7vqXeZP0x+Utx9kB2XZUBqZjp8rc7Bdm45/qU=; b=tT0P2gfIBM66/aJTeoG1Ry7EK5FwTaNH/hlK9HkMVvLN+kVAmmhOdPAi8ELLHeEDCU 0KXraLAtr1n8NyIr/QEri23c7DWrpESf+63g9VTADVPubl7bW1Z+EP6v1tlSB/1JfTXO R2Ee3Q9xlZZBppnEA29QGNXWPd0zDiCL+Bapiw+xtI6AI2WQ+U8EN9bp9+EIOmYICacP LLjt8e6wVyuUViQDMPBq5A0c2uHfEujrgGYPHh7CFpvTFAwqPYkZ3bHCARgdKHyEPw8Y 7asQguu96AFxxFYEsEFKKyTL1HTZRj5YaEsbWrkd1zij4iO1vMkPYzPBe21ixFgCrxOR OsMQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=HFuNCX7vqXeZP0x+Utx9kB2XZUBqZjp8rc7Bdm45/qU=; b=MUK8EN+2eKUV9r6eUZYE6/NCxU6rJnGjxSs8uxVsVwRgeU/1RykwUOEfnvZvxwkHNA 4I2BD2cAkz8lpGI9vJFoUtrz8kR4hSL2VHYeJWdocuHsWBXU2teOsliHSqoP6GHunQKT qm0CvUDYRh8PHjMkw3ZjWQWDNuqSThUzmgetIv5xhEg8QvBkHE4V+umz8cQyzwdQI7CS MsfctzgwPsFUtlyh684m+aD2B+ruC6tQ5+SeRo8Vt+5uPAYsuMDyC0LUCAgujf5iU5qe 2lPuw88leEcgkWf3p0bp9SPFQYWHAs8GRWwm4QddBgW4tfvgaIryBkQDu3N+UJFKuDci qNAg== X-Gm-Message-State: AOAM532z17hWDXdNZf6drMYWSgnxsLjcXz0siVdUQHv3nstCZSFzfUCq 73kaZaChDKbAY1tStxvsMlwWunVQ X-Google-Smtp-Source: ABdhPJz/iOEFhIC/CFRoJ1NFwM7w82wEaRPvuLiln4IJEueHqgu17lX1jCDSmDaz9r2m2Alk9DYwMw== X-Received: by 2002:a63:8f08:: with SMTP id n8mr4130648pgd.9.1596649556565; Wed, 05 Aug 2020 10:45:56 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:400::5:16b0]) by smtp.gmail.com with ESMTPSA id a2sm4840937pfh.152.2020.08.05.10.45.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2020 10:45:54 -0700 (PDT) Date: Wed, 5 Aug 2020 10:45:52 -0700 From: Alexei Starovoitov To: Andrii Nakryiko Cc: Song Liu , open list , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , john fastabend , KP Singh , Jesper Dangaard Brouer , Daniel Xu Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: add benchmark for uprobe vs. user_prog Message-ID: <20200805174552.56q6eauad7glyzgm@ast-mbp.dhcp.thefacebook.com> References: <20200801084721.1812607-1-songliubraving@fb.com> <20200801084721.1812607-6-songliubraving@fb.com> <7384B583-EE19-4045-AC72-B6FE87C187DD@fb.com> <20200805171639.tsqjmifd7eb3htou@ast-mbp.dhcp.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Aug 05, 2020 at 10:27:28AM -0700, Andrii Nakryiko wrote: > On Wed, Aug 5, 2020 at 10:16 AM Alexei Starovoitov > wrote: > > > > On Wed, Aug 05, 2020 at 04:47:30AM +0000, Song Liu wrote: > > > > > > Being able to trigger BPF program on a different CPU could enable many > > > use cases and optimizations. The use case I am looking at is to access > > > perf_event and percpu maps on the target CPU. For example: > > > 0. trigger the program > > > 1. read perf_event on cpu x; > > > 2. (optional) check which process is running on cpu x; > > > 3. add perf_event value to percpu map(s) on cpu x. > > > > If the whole thing is about doing the above then I don't understand why new > > prog type is needed. Can prog_test_run support existing BPF_PROG_TYPE_KPROBE? > > "enable many use cases" sounds vague. I don't think folks reading > > the patches can guess those "use cases". > > "Testing existing kprobe bpf progs" would sound more convincing to me. > > Was just about to propose the same :) I wonder if generic test_run() > capability to trigger test programs of whatever supported type on a > specified CPU through IPI can be added. That way you can even use the > XDP program to do what Song seems to need. > > TRACEPOINTs might also be a good fit here, given it seems simpler to > let users specify custom tracepoint data for test_run(). Having the > ability to unit-test KPROBE and TRACEPOINT, however rudimentary, is > already a big win. > > > If the test_run framework can be extended to trigger kprobe with correct pt_regs. > > As part of it test_run would trigger on a given cpu with $ip pointing > > to some test fuction in test_run.c. For local test_run the stack trace > > would include bpf syscall chain. For IPI the stack trace would include > > the corresponding kernel pieces where top is our special test function. > > Sort of like pseudo kprobe where there is no actual kprobe logic, > > since kprobe prog doesn't care about mechanism. It needs correct > > pt_regs only as input context. > > The kprobe prog output (return value) has special meaning though, > > so may be kprobe prog type is not a good fit. > > It does? I don't remember returning 1 from KPROBE changing anything. I > thought it's only the special bpf_override_return() that can influence > the kernel function return result. See comment in trace_call_bpf(). And logic to handle it in kprobe_perf_func() for kprobes. and in perf_trace_run_bpf_submit() for tracepoints. It's historical and Song actually discovered an issue with such behavior. I don't remember whether we've concluded on the solution.