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00:04:45 +0000 Message-ID: <5d363ea7-16c6-b8e8-b6ee-11cbe9bf1cf2@fb.com> Date: Wed, 24 Nov 2021 16:04:42 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.3.2 Subject: Re: [PATCH v2 bpf-next 4/4] selftest/bpf/benchs: add bpf_loop benchmark Content-Language: en-US To: =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Andrii Nakryiko CC: bpf , Andrii Nakryiko , Alexei Starovoitov , Daniel Borkmann , Kernel Team References: <20211123183409.3599979-1-joannekoong@fb.com> <20211123183409.3599979-5-joannekoong@fb.com> <87y25ebry1.fsf@toke.dk> <3eaa1a93-c3f1-830a-b711-117b27102cc5@fb.com> <87r1b5btl0.fsf@toke.dk> <87lf1db4gh.fsf@toke.dk> From: Joanne Koong In-Reply-To: <87lf1db4gh.fsf@toke.dk> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: MW4PR04CA0364.namprd04.prod.outlook.com (2603:10b6:303:81::9) To SA1PR15MB4465.namprd15.prod.outlook.com (2603:10b6:806:194::23) MIME-Version: 1.0 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X-OriginatorOrg: fb.com X-Proofpoint-ORIG-GUID: 5wMEbfVwaSFKupiB2NYmzV51jwdAUDdE X-Proofpoint-GUID: 5wMEbfVwaSFKupiB2NYmzV51jwdAUDdE X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.790,Hydra:6.0.425,FMLib:17.0.607.475 definitions=2021-11-24_06,2021-11-24_01,2020-04-07_01 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 impostorscore=0 mlxscore=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 spamscore=0 malwarescore=0 bulkscore=0 adultscore=0 priorityscore=1501 phishscore=0 mlxlogscore=946 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2110150000 definitions=main-2111240116 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 11/24/21 1:59 PM, Toke Høiland-Jørgensen wrote: > Andrii Nakryiko writes: > >> On Wed, Nov 24, 2021 at 4:56 AM Toke Høiland-Jørgensen wrote: >>> Joanne Koong writes: >>> >>>> On 11/23/21 11:19 AM, Toke Høiland-Jørgensen wrote: >>>> >>>>> Joanne Koong writes: >>>>> >>>>>> Add benchmark to measure the throughput and latency of the bpf_loop >>>>>> call. >>>>>> >>>>>> Testing this on qemu on my dev machine on 1 thread, the data is >>>>>> as follows: >>>>>> >>>>>> nr_loops: 1 >>>>>> bpf_loop - throughput: 43.350 ± 0.864 M ops/s, latency: 23.068 ns/op >>>>>> >>>>>> nr_loops: 10 >>>>>> bpf_loop - throughput: 69.586 ± 1.722 M ops/s, latency: 14.371 ns/op >>>>>> >>>>>> nr_loops: 100 >>>>>> bpf_loop - throughput: 72.046 ± 1.352 M ops/s, latency: 13.880 ns/op >>>>>> >>>>>> nr_loops: 500 >>>>>> bpf_loop - throughput: 71.677 ± 1.316 M ops/s, latency: 13.951 ns/op >>>>>> >>>>>> nr_loops: 1000 >>>>>> bpf_loop - throughput: 69.435 ± 1.219 M ops/s, latency: 14.402 ns/op >>>>>> >>>>>> nr_loops: 5000 >>>>>> bpf_loop - throughput: 72.624 ± 1.162 M ops/s, latency: 13.770 ns/op >>>>>> >>>>>> nr_loops: 10000 >>>>>> bpf_loop - throughput: 75.417 ± 1.446 M ops/s, latency: 13.260 ns/op >>>>>> >>>>>> nr_loops: 50000 >>>>>> bpf_loop - throughput: 77.400 ± 2.214 M ops/s, latency: 12.920 ns/op >>>>>> >>>>>> nr_loops: 100000 >>>>>> bpf_loop - throughput: 78.636 ± 2.107 M ops/s, latency: 12.717 ns/op >>>>>> >>>>>> nr_loops: 500000 >>>>>> bpf_loop - throughput: 76.909 ± 2.035 M ops/s, latency: 13.002 ns/op >>>>>> >>>>>> nr_loops: 1000000 >>>>>> bpf_loop - throughput: 77.636 ± 1.748 M ops/s, latency: 12.881 ns/op >>>>>> >>>>>> From this data, we can see that the latency per loop decreases as the >>>>>> number of loops increases. On this particular machine, each loop had an >>>>>> overhead of about ~13 ns, and we were able to run ~70 million loops >>>>>> per second. >>>>> The latency figures are great, thanks! I assume these numbers are with >>>>> retpolines enabled? Otherwise 12ns seems a bit much... Or is this >>>>> because of qemu? >>>> I just tested it on a machine (without retpoline enabled) that runs on >>>> actual >>>> hardware and here is what I found: >>>> >>>> nr_loops: 1 >>>> bpf_loop - throughput: 46.780 ± 0.064 M ops/s, latency: 21.377 ns/op >>>> >>>> nr_loops: 10 >>>> bpf_loop - throughput: 198.519 ± 0.155 M ops/s, latency: 5.037 ns/op >>>> >>>> nr_loops: 100 >>>> bpf_loop - throughput: 247.448 ± 0.305 M ops/s, latency: 4.041 ns/op >>>> >>>> nr_loops: 500 >>>> bpf_loop - throughput: 260.839 ± 0.380 M ops/s, latency: 3.834 ns/op >>>> >>>> nr_loops: 1000 >>>> bpf_loop - throughput: 262.806 ± 0.629 M ops/s, latency: 3.805 ns/op >>>> >>>> nr_loops: 5000 >>>> bpf_loop - throughput: 264.211 ± 1.508 M ops/s, latency: 3.785 ns/op >>>> >>>> nr_loops: 10000 >>>> bpf_loop - throughput: 265.366 ± 3.054 M ops/s, latency: 3.768 ns/op >>>> >>>> nr_loops: 50000 >>>> bpf_loop - throughput: 235.986 ± 20.205 M ops/s, latency: 4.238 ns/op >>>> >>>> nr_loops: 100000 >>>> bpf_loop - throughput: 264.482 ± 0.279 M ops/s, latency: 3.781 ns/op >>>> >>>> nr_loops: 500000 >>>> bpf_loop - throughput: 309.773 ± 87.713 M ops/s, latency: 3.228 ns/op >>>> >>>> nr_loops: 1000000 >>>> bpf_loop - throughput: 262.818 ± 4.143 M ops/s, latency: 3.805 ns/op >>>> >>>> The latency is about ~4ns / loop. >>>> >>>> I will update the commit message in v3 with these new numbers as well. >>> Right, awesome, thank you for the additional test. This is closer to >>> what I would expect: on the hardware I'm usually testing on, a function >>> call takes ~1.5ns, but the difference might just be the hardware, or >>> because these are indirect calls. >>> >>> Another comparison just occurred to me (but it's totally OK if you don't >>> want to add any more benchmarks): >>> >>> The difference between a program that does: >>> >>> bpf_loop(nr_loops, empty_callback, NULL, 0); >>> >>> and >>> >>> for (i = 0; i < nr_loops; i++) >>> empty_callback(); >> You are basically trying to measure the overhead of bpf_loop() helper >> call itself, because other than that it should be identical. > No, I'm trying to measure the difference between the indirect call in > the helper, and the direct call from the BPF program. Should be minor > without retpolines, and somewhat higher where they are enabled... > >> We can estimate that already from the numbers Joanne posted above: >> >> nr_loops: 1 >> bpf_loop - throughput: 46.780 ± 0.064 M ops/s, latency: 21.377 ns/op >> nr_loops: 1000 >> bpf_loop - throughput: 262.806 ± 0.629 M ops/s, latency: 3.805 ns/op >> >> nr_loops:1 is bpf_loop() overhead and one static callback call. >> bpf_loop()'s own overhead will be in the ballpark of 21.4 - 3.8 = >> 17.6ns. I don't think we need yet another benchmark just for this. > That seems really high, though? The helper is a pretty simple function, > and the call to it should just be JIT'ed into a single regular function > call, right? So why the order-of-magnitude difference? I think the overhead of triggering the bpf program from the userspace benchmarking program is also contributing to this. When nr_loops = 1, we have to do the context switch between userspace + kernel per every 1000 loops; this overhead also contributes to the latency numbers above > -Toke >