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=-12.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 9703BC43460 for ; Wed, 7 Apr 2021 18:31:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5803C6120E for ; Wed, 7 Apr 2021 18:31:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355349AbhDGScF (ORCPT ); Wed, 7 Apr 2021 14:32:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229970AbhDGScD (ORCPT ); Wed, 7 Apr 2021 14:32:03 -0400 Received: from mail-yb1-xb29.google.com (mail-yb1-xb29.google.com [IPv6:2607:f8b0:4864:20::b29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0864C06175F; Wed, 7 Apr 2021 11:31:53 -0700 (PDT) Received: by mail-yb1-xb29.google.com with SMTP id e188so10166049ybb.13; Wed, 07 Apr 2021 11:31:53 -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=Kn69rhRMMVrayDs5H+UzYud2Z7b87MPu6OYNo7BSq9A=; b=Q2cgRQjRQoFVUE6O76KGZGQ0T10GT/8WWUQ4aLFIvZB1FdDAVI7p0zTOtKA3w5gmxC GJ9+qEn9Pl6LOQDUOz/2AscK4HGX/1pzTtrWrclrliS9UWu2vetCXRLORs9r1/0BGOll z4+IUGKVMpbbjvfjr/Cer+mqJQIqGPMQaVcF5Wyn9jFeVGrczf9AvISUdu3E3Z08gfCa tqIR2B9NeRkhhNaVWenAAVcYue4UsqlMAHKD8aTXMxbjTHbTowFcZ9tqnt9JmYZmEz7E /9dWXUufoX7o7RKzVcI7hhwlnKcS3T8x6l6I9Z/4vTJoPub06WYZ4jEsnzbDbBkuD1Tm E7bw== 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=Kn69rhRMMVrayDs5H+UzYud2Z7b87MPu6OYNo7BSq9A=; b=tjp51UgVsUw9dveE7K+1oE+bd3Ctnq4pJWYA80F2s6HXG/IPD6zUI1wBC5aQ09xQ24 aLD50NVBF0W3F/VorcOvnLwIkztiN/jne3Yx12u/0sEQvqHKqTmktiD7nHPa3NsoxP65 /20f+ukdNa15M93YFwfoPnVJ1HMx/QrnvPkLVFsGUPGRZjdtNURNhdpL0JTJf4xhVUWx lHgurknNNJ8op4EfRYXJqhWG9U7ORFdhNcA1tDZ8ZvY2iBxSA999yUS5tA3dZ4m9U4LV b2A408wYtpDIbCDVr+ciAS6DqKHZ+EJPyVrm4E1sVOfX2d9uVeiorzisCFwp5CfQj4Bz GHmA== X-Gm-Message-State: AOAM532eVSixlRrilev70gKpirjFw1UwiE5lI6tmv/ZWNOjEi6qHK1GH kA1uc41GWFfz5BAHqpgFgXp2jQIqm+IdmCtEC1c= X-Google-Smtp-Source: ABdhPJwyD46iJ/cTYmc9rpHBrMJfjKJ5VR+417ZI8GKSj4oYvi0t0OHizfMM7YPKvVsq94rSk7oftNhfxDjL2qjXeCo= X-Received: by 2002:a25:9942:: with SMTP id n2mr6307629ybo.230.1617820312912; Wed, 07 Apr 2021 11:31:52 -0700 (PDT) MIME-Version: 1.0 References: <20210406185400.377293-1-pctammela@mojatatu.com> <20210406185400.377293-3-pctammela@mojatatu.com> In-Reply-To: <20210406185400.377293-3-pctammela@mojatatu.com> From: Andrii Nakryiko Date: Wed, 7 Apr 2021 11:31:42 -0700 Message-ID: Subject: Re: [PATCH bpf-next v2 2/3] libbpf: selftests: refactor 'BPF_PERCPU_TYPE()' and 'bpf_percpu()' macros To: Pedro Tammela Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Shuah Khan , Pedro Tammela , Matthieu Baerts , David Verbeiren , "open list:BPF (Safe dynamic programs and tools)" , "open list:BPF (Safe dynamic programs and tools)" , open list , "open list:KERNEL SELFTEST FRAMEWORK" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 6, 2021 at 11:55 AM Pedro Tammela wrote: > > This macro was refactored out of the bpf selftests. > > Since percpu values are rounded up to '8' in the kernel, a careless > user in userspace might encounter unexpected values when parsing the > output of the batched operations. I wonder if a user has to be more careful, though? This BPF_PERCPU_TYPE, __bpf_percpu_align and bpf_percpu macros seem to create just another opaque layer. It actually seems detrimental to me. I'd rather emphasize in the documentation (e.g., in bpf_map_lookup_elem) that all per-cpu maps are aligning values at 8 bytes, so user has to make sure that array of values provided to bpf_map_lookup_elem() has each element size rounded up to 8. In practice, I'd recommend users to always use __u64/__s64 when having primitive integers in a map (they are not saving anything by using int, it just creates an illusion of savings). Well, maybe on 32-bit arches they would save a bit of CPU, but not on typical 64-bit architectures. As for using structs as values, always mark them as __attribute__((aligned(8))). Basically, instead of obscuring the real use some more, let's clarify and maybe even provide some examples in documentation? > > Now that both array and hash maps have support for batched ops in the > percpu variant, let's provide a convenient macro to declare percpu map > value types. > > Updates the tests to a "reference" usage of the new macro. > > Signed-off-by: Pedro Tammela > --- > tools/lib/bpf/bpf.h | 10 ++++ > tools/testing/selftests/bpf/bpf_util.h | 7 --- > .../bpf/map_tests/htab_map_batch_ops.c | 48 ++++++++++--------- > .../selftests/bpf/prog_tests/map_init.c | 5 +- > tools/testing/selftests/bpf/test_maps.c | 16 ++++--- > 5 files changed, 46 insertions(+), 40 deletions(-) > [...] > @@ -400,11 +402,11 @@ static void test_arraymap(unsigned int task, void *data) > static void test_arraymap_percpu(unsigned int task, void *data) > { > unsigned int nr_cpus = bpf_num_possible_cpus(); > - BPF_DECLARE_PERCPU(long, values); > + pcpu_map_value_t values[nr_cpus]; > int key, next_key, fd, i; > > fd = bpf_create_map(BPF_MAP_TYPE_PERCPU_ARRAY, sizeof(key), > - sizeof(bpf_percpu(values, 0)), 2, 0); > + sizeof(long), 2, 0); > if (fd < 0) { > printf("Failed to create arraymap '%s'!\n", strerror(errno)); > exit(1); > @@ -459,7 +461,7 @@ static void test_arraymap_percpu(unsigned int task, void *data) > static void test_arraymap_percpu_many_keys(void) > { > unsigned int nr_cpus = bpf_num_possible_cpus(); This just sets a bad example for anyone using selftests as an aspiration for their own code. bpf_num_possible_cpus() does exit(1) internally if libbpf_num_possible_cpus() returns error. No one should write real production code like that. So maybe let's provide a better example instead with error handling and malloc (or perhaps alloca)? > - BPF_DECLARE_PERCPU(long, values); > + pcpu_map_value_t values[nr_cpus]; > /* nr_keys is not too large otherwise the test stresses percpu > * allocator more than anything else > */ > @@ -467,7 +469,7 @@ static void test_arraymap_percpu_many_keys(void) > int key, fd, i; > > fd = bpf_create_map(BPF_MAP_TYPE_PERCPU_ARRAY, sizeof(key), > - sizeof(bpf_percpu(values, 0)), nr_keys, 0); > + sizeof(long), nr_keys, 0); > if (fd < 0) { > printf("Failed to create per-cpu arraymap '%s'!\n", > strerror(errno)); > -- > 2.25.1 >