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Tue, 12 May 2020 15:11:36 +0000 Subject: Re: [PATCH v2 bpf-next 2/3] selftest/bpf: fmod_ret prog and implement test_overhead as part of bench To: Andrii Nakryiko CC: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team , John Fastabend References: <20200508232032.1974027-1-andriin@fb.com> <20200508232032.1974027-3-andriin@fb.com> From: Yonghong Song Message-ID: Date: Tue, 12 May 2020 08:11:33 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BYAPR21CA0008.namprd21.prod.outlook.com (2603:10b6:a03:114::18) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from macbook-pro-52.local.dhcp.thefacebook.com (2620:10d:c090:400::5:d0f0) by BYAPR21CA0008.namprd21.prod.outlook.com (2603:10b6:a03:114::18) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3021.2 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: f31b7cc6-77c5-4bd5-7dd1-08d7f686c377 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 May 2020 15:11:36.4711 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: PrNPwiNhSaIINtGIHbln/rOi72eo5erBWNh2zYYcqmWyNssOysdDSRHkFP/vIaLr X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3432 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.676 definitions=2020-05-12_04:2020-05-11,2020-05-12 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 spamscore=0 impostorscore=0 suspectscore=0 adultscore=0 phishscore=0 bulkscore=0 clxscore=1015 malwarescore=0 mlxlogscore=794 priorityscore=1501 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2005120115 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 5/11/20 9:22 PM, Andrii Nakryiko wrote: > On Sat, May 9, 2020 at 10:24 AM Yonghong Song wrote: >> >> >> >> On 5/8/20 4:20 PM, Andrii Nakryiko wrote: >>> Add fmod_ret BPF program to existing test_overhead selftest. Also re-implement >>> user-space benchmarking part into benchmark runner to compare results. Results >>> with ./bench are consistently somewhat lower than test_overhead's, but relative >>> performance of various types of BPF programs stay consisten (e.g., kretprobe is >>> noticeably slower). >>> >>> run_bench_rename.sh script (in benchs/ directory) was used to produce the >>> following numbers: >>> >>> base : 3.975 ± 0.065M/s >>> kprobe : 3.268 ± 0.095M/s >>> kretprobe : 2.496 ± 0.040M/s >>> rawtp : 3.899 ± 0.078M/s >>> fentry : 3.836 ± 0.049M/s >>> fexit : 3.660 ± 0.082M/s >>> fmodret : 3.776 ± 0.033M/s >>> >>> While running test_overhead gives: >>> >>> task_rename base 4457K events per sec >>> task_rename kprobe 3849K events per sec >>> task_rename kretprobe 2729K events per sec >>> task_rename raw_tp 4506K events per sec >>> task_rename fentry 4381K events per sec >>> task_rename fexit 4349K events per sec >>> task_rename fmod_ret 4130K events per sec >> >> Do you where the overhead is and how we could provide options in >> bench to reduce the overhead so we can achieve similar numbers? >> For benchmarking, sometimes you really want to see "true" >> potential of a particular implementation. > > Alright, let's make it an official bench-off... :) And the reason for > this discrepancy, turns out to be... not atomics at all! But rather a > single-threaded vs multi-threaded process (well, at least task_rename > happening from non-main thread, I didn't narrow it down further). It would be good to find out why and have a scheme (e.g. some kind of affinity binding) to close the gap. > Atomics actually make very little difference, which gives me a good > peace of mind :) > > So, I've built and ran test_overhead (selftest) and bench both as > multi-threaded and single-threaded apps. Corresponding results match > almost perfectly. And that's while test_overhead doesn't use atomics > at all, while bench still does. Then I also ran test_overhead with > added generics to match bench implementation. There are barely any > differences, see two last sets of results. > > BTW, selftest results seems bit lower from the ones in original > commit, probably because I made it run more iterations (like 40 times > more) to have more stable results. > > So here are the results: > > Single-threaded implementations > =============================== > > /* bench: single-threaded, atomics */ > base : 4.622 ± 0.049M/s > kprobe : 3.673 ± 0.052M/s > kretprobe : 2.625 ± 0.052M/s > rawtp : 4.369 ± 0.089M/s > fentry : 4.201 ± 0.558M/s > fexit : 4.309 ± 0.148M/s > fmodret : 4.314 ± 0.203M/s > > /* selftest: single-threaded, no atomics */ > task_rename base 4555K events per sec > task_rename kprobe 3643K events per sec > task_rename kretprobe 2506K events per sec > task_rename raw_tp 4303K events per sec > task_rename fentry 4307K events per sec > task_rename fexit 4010K events per sec > task_rename fmod_ret 3984K events per sec > > > Multi-threaded implementations > ============================== > > /* bench: multi-threaded w/ atomics */ > base : 3.910 ± 0.023M/s > kprobe : 3.048 ± 0.037M/s > kretprobe : 2.300 ± 0.015M/s > rawtp : 3.687 ± 0.034M/s > fentry : 3.740 ± 0.087M/s > fexit : 3.510 ± 0.009M/s > fmodret : 3.485 ± 0.050M/s > > /* selftest: multi-threaded w/ atomics */ > task_rename base 3872K events per sec > task_rename kprobe 3068K events per sec > task_rename kretprobe 2350K events per sec > task_rename raw_tp 3731K events per sec > task_rename fentry 3639K events per sec > task_rename fexit 3558K events per sec > task_rename fmod_ret 3511K events per sec > > /* selftest: multi-threaded, no atomics */ > task_rename base 3945K events per sec > task_rename kprobe 3298K events per sec > task_rename kretprobe 2451K events per sec > task_rename raw_tp 3718K events per sec > task_rename fentry 3782K events per sec > task_rename fexit 3543K events per sec > task_rename fmod_ret 3526K events per sec > > [...]