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 D38A5C433DF for ; Wed, 5 Aug 2020 17:30:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB7F622D37 for ; Wed, 5 Aug 2020 17:30:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="nb7391sF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728114AbgHERa0 (ORCPT ); Wed, 5 Aug 2020 13:30:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53236 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728788AbgHER1k (ORCPT ); Wed, 5 Aug 2020 13:27:40 -0400 Received: from mail-yb1-xb42.google.com (mail-yb1-xb42.google.com [IPv6:2607:f8b0:4864:20::b42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC804C061575; Wed, 5 Aug 2020 10:27:39 -0700 (PDT) Received: by mail-yb1-xb42.google.com with SMTP id x2so4035803ybf.12; Wed, 05 Aug 2020 10:27:39 -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; bh=BUORAD323AYH3zxx1yaS/aYxJilBT0bejXUe4CU1IsU=; b=nb7391sFHHARlePNt23uWFUiCgJDNofextE1aito4sTSYWdJoc/yW7awE7AwDekIQy nQMdw7M56WSttzqnt4r/rinYc+iholmrAs7j82PJhz9OyuE2x/UDuIptCwy+aAUe/sc3 sdtBKtVW+qtwEkNoyEUWTlvt01nHEyrNTAccsXcBausvwY9lV3kNzseWdWRWUtpBf4vn vzKszBu0NEbXGrPfS4t/lH+3P7PxcrEKLJR29/MG5j281+Hfmh49/8/4XbVjVcnKcE72 Bx+120NdmYBdfsL53Mxn9gS4y1TRSKlUMPMNKievyfxEQ22EH7gDVg375zEA+oMC3NRR AOog== 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; bh=BUORAD323AYH3zxx1yaS/aYxJilBT0bejXUe4CU1IsU=; b=mU25JNlQ0WbPKa7k0gKFBqalEON1tO+EE3nK4Qj+H+g9EbqZtghfIkZm4HH3s9ABLt nKY0XOvgIwmiY2FhUTr9g5jmWty/zyOzfRqBn94qcQSrVIlPQGZ3y/U6uNm7UJqBXTT1 tRtsfSwTCWyBcrk6f8yNX8Oz23fJ0JdEmTimRxBHgFad7OyMGwPbr2IJx1+SEi7yQiKI Ms5g2YafQApTE1OFHNA9w7gOxEbwJFL427igAoBvR5FpjlzI7SQfUTh1omZI6kQ2focH iUXxwuep1Rz6RlMCzqWKRlvEjXLig06uFjNM0XxMHG6F5b6K59ZMW5zknaN6RIaOWWx6 yNSA== X-Gm-Message-State: AOAM533NVlK8SyNGepOAlQ6A2SMjP1sn/MTFN5RpiM/w1njadRIbdaS0 6rScp2wsuSMbTQS1Bn2WA5unEvOq9kEgxbq0HFk= X-Google-Smtp-Source: ABdhPJzV/vqVTpcSUL8lQmokCDonYTJ8sM2iojmyXsyq64VdK2J/hLo3FUzGE0OyGsfWug1unqWO9IDmfJ0pgr3dC+s= X-Received: by 2002:a25:2ad3:: with SMTP id q202mr6206874ybq.27.1596648459142; Wed, 05 Aug 2020 10:27:39 -0700 (PDT) MIME-Version: 1.0 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> In-Reply-To: <20200805171639.tsqjmifd7eb3htou@ast-mbp.dhcp.thefacebook.com> From: Andrii Nakryiko Date: Wed, 5 Aug 2020 10:27:28 -0700 Message-ID: Subject: Re: [PATCH bpf-next 5/5] selftests/bpf: add benchmark for uprobe vs. user_prog To: Alexei Starovoitov Cc: Song Liu , open list , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , john fastabend , KP Singh , Jesper Dangaard Brouer , Daniel Xu Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org 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. > Something like fentry/fexit may be better, since verifier check_return_code() > enforces 'return 0'. So their return value is effectively "void". > Then prog_test_run would need to gain an ability to trigger > fentry/fexit prog on a given cpu.