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charset="us-ascii" Content-ID: <397ED8892C594846B3E7DAB69704FD26@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: BYAPR15MB2999.namprd15.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: d3cbd6ed-4344-4488-89c6-08d9375da100 X-MS-Exchange-CrossTenant-originalarrivaltime: 24 Jun 2021 22:15:52.0550 (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: QzFn+PGPhzRhfk81bFZOjFOZw8QTMghYwQV921kJnNW4MtEYhQPLcmzy9pDCn+ZKr1JzJy6kfvQpjWseroARFg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR15MB3667 X-OriginatorOrg: fb.com X-Proofpoint-GUID: P_VQHBU9tojwCSJ9kFMsDo4Ry8dzDNCo X-Proofpoint-ORIG-GUID: P_VQHBU9tojwCSJ9kFMsDo4Ry8dzDNCo X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-06-24_16:2021-06-24,2021-06-24 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 phishscore=0 impostorscore=0 mlxlogscore=999 priorityscore=1501 lowpriorityscore=0 adultscore=0 spamscore=0 malwarescore=0 bulkscore=0 suspectscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106240124 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Jun 24, 2021, at 3:06 PM, Namhyung Kim wrote: >=20 > On Thu, Jun 24, 2021 at 2:41 PM Song Liu wrote: >>=20 >>=20 >>=20 >>> On Jun 24, 2021, at 2:01 PM, Namhyung Kim wrote: >>>=20 >>> On Thu, Jun 24, 2021 at 9:20 AM Song Liu wrote: >>>>>>> + >>>>>>> +// single set of global perf events to measure >>>>>>> +struct { >>>>>>> + __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); >>>>>>> + __uint(key_size, sizeof(__u32)); >>>>>>> + __uint(value_size, sizeof(int)); >>>>>>> + __uint(max_entries, 1); >>>>>>> +} events SEC(".maps"); >>>>>>> + >>>>>>> +// from logical cpu number to event index >>>>>>> +// useful when user wants to count subset of cpus >>>>>>> +struct { >>>>>>> + __uint(type, BPF_MAP_TYPE_HASH); >>>>>>> + __uint(key_size, sizeof(__u32)); >>>>>>> + __uint(value_size, sizeof(__u32)); >>>>>>> + __uint(max_entries, 1); >>>>>>> +} cpu_idx SEC(".maps"); >>>>>>=20 >>>>>> How about we make cpu_idx a percpu array and use 0,1 for >>>>>> disable/enable profiling on this cpu? >>>>>=20 >>>>> No, it's to calculate an index to the cgrp_readings map which >>>>> has the event x cpu x cgroup number of elements. >>>>>=20 >>>>> It controls enabling events with a global (bss) variable. >>>>=20 >>>> If we make cgrp_idx a per cpu array, we probably don't need the >>>> cpu_idx map? >>>=20 >>> Right. >=20 > Maybe not. Sometimes we want to profile a subset of cpus only. > In that case, cpu !=3D idx then I think we still need this. We can only attach the bpf program on selected CPUs. Say, we want CPUs 1, 3, 5. We just do=20 for (i in [1, 3, 5]) { link =3D bpf_program__attach_perf_event(skel->progs.on_switch, FD(cgrp_switch, i)); /* */ } The value arrays are still for all cpu, but they will just report zero for CPU 0, 2, 4, ....=20 Would this work?=20 =09 [...] >>>>> Maybe. But I don't know how to access the elements >>>>> in a per-cpu map from userspace. >>>>=20 >>>> Please refer to bperf__read() reading accum_readings. Basically, we re= ad >>>> one index of all CPUs with one bpf_map_lookup_elem(). >>>=20 >>> Thanks! So when I use a per-cpu array with 3 elements, I can access >>> to cpu/elem entries in a row like below, right? >>>=20 >>> 0/0, 0/1, 0/2, 1/0, 1/1, 1/2, 2/0, 2/1, 2/2, 3/0, ... >>=20 >> I am not sure I am following here. >>=20 >> Say the system have 10 cpus, and the array has 3 elements. We can do: >>=20 >> __u32 values[10]; /* assuming both key and value are __u32 */ >> __u32 elem; >> int cpu; >>=20 >> for (elem =3D 0; elem < 3; elem++) { >> bpf_map_lookup_elem(map_fd, &elem, values); >> for (cpu =3D 0; cpu < 10; cpu++) >> values[cpu] /* this is the value for cpu/elem */ >> } >=20 > Thanks for the explanation, I didn't think that way. > I thought it like below: >=20 > __u32 elem, value; >=20 > for (elem =3D 0; elem < 3 * 10; elem++) { > bpf_map_lookup_elem(map_fd, &elem, &value); > } >=20 > So in this case, the actual value size is like below, right? >=20 > value-size =3D map-value-size * number-of-cpu This is right (for user space).=20 Thanks, Song