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charset="us-ascii" Content-ID: <5A7CE62B465BC2408D707E9B5F36875D@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: 1a8017c0-132d-429e-6102-08d7826d5511 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Dec 2019 21:17:19.2979 (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: RSZJgqx8QHOkcqh6CCmkfrUnRxObcjbYcbF2QV+v0EEeKHPVxRN0v2pGEXFJ61nm X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR15MB2896 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2019-12-16_07:2019-12-16,2019-12-16 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 lowpriorityscore=0 malwarescore=0 spamscore=0 impostorscore=0 clxscore=1015 adultscore=0 bulkscore=0 mlxlogscore=365 phishscore=0 suspectscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-1912160178 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Dec 16, 2019 at 11:33:01AM -0800, Eric Dumazet wrote: >=20 >=20 > On 12/16/19 11:14 AM, Martin Lau wrote: > > On Fri, Dec 13, 2019 at 05:59:54PM -0800, Eric Dumazet wrote: > >> > >> > >> On 12/13/19 4:47 PM, Martin KaFai Lau wrote: > >>> This patch adds a helper to handle jiffies. Some of the > >>> tcp_sock's timing is stored in jiffies. Although things > >>> could be deduced by CONFIG_HZ, having an easy way to get > >>> jiffies will make the later bpf-tcp-cc implementation easier. > >>> > >> > >> ... > >> > >>> + > >>> +BPF_CALL_2(bpf_jiffies, u64, in, u64, flags) > >>> +{ > >>> + if (!flags) > >>> + return get_jiffies_64(); > >>> + > >>> + if (flags & BPF_F_NS_TO_JIFFIES) { > >>> + return nsecs_to_jiffies(in); > >>> + } else if (flags & BPF_F_JIFFIES_TO_NS) { > >>> + if (!in) > >>> + in =3D get_jiffies_64(); > >>> + return jiffies_to_nsecs(in); > >>> + } > >>> + > >>> + return 0; > >>> +} > >> > >> This looks a bit convoluted :) > >> > >> Note that we could possibly change net/ipv4/tcp_cubic.c to no longer u= se jiffies at all. > >> > >> We have in tp->tcp_mstamp an accurate timestamp (in usec) that can be = converted to ms. > > Thanks for the feedbacks! > >=20 > > I have a few questions that need some helps. > >=20 > > Does it mean tp->tcp_mstamp can be used as the "now" in cubic? >=20 > TCP makes sure to update tp->tcp_mstamp at least once when handling > a particular packet. We did that to avoid calling possibly expensive > kernel time service (Some platforms do not have fast TSC)=20 >=20 > > or tcp_clock_ns() should still be called in cubic, e.g. to replace > > bictcp_clock() and tcp_jiffies32? >=20 > Yeah, there is this lsndtime and tcp_jiffies32 thing, but maybe > we can find a way to fetch jiffies32 without having to call a bpf helper = ? Loading a kernel global variable is not yet supported. Thus, helper is needed but it could be inlined like array_map_gen_lookup().