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charset="us-ascii" Content-ID: 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: d7e1b459-04bb-4b35-71c5-08d8f600cae7 X-MS-Exchange-CrossTenant-originalarrivaltime: 02 Apr 2021 17:57:33.6444 (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: yBQ6bX3xWGzo91jB93td4m6JPRHzClaoqQ4ljSGvl3MCkVx0/u8KPFdGhafkXHbTmwN9tRjs8ErKsqKur9RJ4A== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2693 X-OriginatorOrg: fb.com X-Proofpoint-GUID: BSch-8UTkxSWcAQj6jbOcCoj25TWEDxi X-Proofpoint-ORIG-GUID: BSch-8UTkxSWcAQj6jbOcCoj25TWEDxi X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-04-02_12:2021-04-01,2021-04-02 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 impostorscore=0 mlxlogscore=999 clxscore=1015 priorityscore=1501 mlxscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 spamscore=0 phishscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2103310000 definitions=main-2104020125 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org > On Apr 2, 2021, at 10:34 AM, Cong Wang wrote: >=20 > On Thu, Apr 1, 2021 at 1:17 PM Song Liu wrote: >>=20 >>=20 >>=20 >>> On Apr 1, 2021, at 10:28 AM, Cong Wang wrote= : >>>=20 >>> On Wed, Mar 31, 2021 at 11:38 PM Song Liu wrote= : >>>>=20 >>>>=20 >>>>=20 >>>>> On Mar 31, 2021, at 9:26 PM, Cong Wang wro= te: >>>>>=20 >>>>> From: Cong Wang >>>>>=20 >>>>> (This patch is still in early stage and obviously incomplete. I am se= nding >>>>> it out to get some high-level feedbacks. Please kindly ignore any cod= ing >>>>> details for now and focus on the design.) >>>>=20 >>>> Could you please explain the use case of the timer? Is it the same as >>>> earlier proposal of BPF_MAP_TYPE_TIMEOUT_HASH? >>>>=20 >>>> Assuming that is the case, I guess the use case is to assign an expire >>>> time for each element in a hash map; and periodically remove expired >>>> element from the map. >>>>=20 >>>> If this is still correct, my next question is: how does this compare >>>> against a user space timer? Will the user space timer be too slow? >>>=20 >>> Yes, as I explained in timeout hashmap patchset, doing it in user-space >>> would require a lot of syscalls (without batching) or copying (with bat= ching). >>> I will add the explanation here, in case people miss why we need a time= r. >>=20 >> How about we use a user space timer to trigger a BPF program (e.g. use >> BPF_PROG_TEST_RUN on a raw_tp program); then, in the BPF program, we can >> use bpf_for_each_map_elem and bpf_map_delete_elem to scan and update the >> map? With this approach, we only need one syscall per period. >=20 > Interesting, I didn't know we can explicitly trigger a BPF program runnin= g > from user-space. Is it for testing purposes only? This is not only for testing. We will use this in perf (starting in 5.13). /* currently in Arnaldo's tree, tools/perf/util/bpf_counter.c: */ /* trigger the leader program on a cpu */ static int bperf_trigger_reading(int prog_fd, int cpu) { DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts, .ctx_in =3D NULL, .ctx_size_in =3D 0, .flags =3D BPF_F_TEST_RUN_ON_CPU, .cpu =3D cpu, .retval =3D 0, ); return bpf_prog_test_run_opts(prog_fd, &opts); } test_run also passes return value (retval) back to user space, so we and=20 adjust the timer interval based on retval. Also, test_run can trigger the program on a specific cpu. This might be=20 useful with percpu map (BPF_MAP_TYPE_PERCPU_HASH, etc.).=20 Thanks, Song