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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: 3d708814-6dbf-46c7-922b-08d8f54b37c2 X-MS-Exchange-CrossTenant-originalarrivaltime: 01 Apr 2021 20:17:47.6857 (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: pAwcic/5UV+fRJvcxSwzP8ZEzeXiPHBH5z/oSTRV+tipngqZwCTkfFWhhApzwxIN320YRw8Dl8S2X9MDQFWZdA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2197 X-OriginatorOrg: fb.com X-Proofpoint-GUID: wz0sCmYydJMSnTRrTWbBhDe3WfpAhwTg X-Proofpoint-ORIG-GUID: wz0sCmYydJMSnTRrTWbBhDe3WfpAhwTg X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.369,18.0.761 definitions=2021-04-01_10:2021-04-01,2021-04-01 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 adultscore=0 suspectscore=0 impostorscore=0 malwarescore=0 phishscore=0 lowpriorityscore=0 mlxlogscore=999 priorityscore=1501 mlxscore=0 bulkscore=0 clxscore=1015 spamscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2103310000 definitions=main-2104010131 X-FB-Internal: deliver Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org > 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 wrote= : >>>=20 >>> From: Cong Wang >>>=20 >>> (This patch is still in early stage and obviously incomplete. I am send= ing >>> it out to get some high-level feedbacks. Please kindly ignore any codin= g >>> 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 batch= ing). > I will add the explanation here, in case people miss why we need a timer. How about we use a user space timer to trigger a BPF program (e.g. use=20 BPF_PROG_TEST_RUN on a raw_tp program); then, in the BPF program, we can=20 use bpf_for_each_map_elem and bpf_map_delete_elem to scan and update the=20 map? With this approach, we only need one syscall per period.=20 Thanks, Song