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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?6+QxeVtSVfwgED+kFDLB2gSqO9aVNTDtxptPk26EFTp1uAxcidkdpigEhHHm?= =?us-ascii?Q?b0WigUmsE0x1SLtRd4qKt2/9XBZJpAAPpArV3q5I/1zI1J0l9fuH/Z+7jShA?= =?us-ascii?Q?bRSjuOYquDzNwJb253AKlEu4Uw+/XfJR688ogiLzH9Uic00f8ZBAirjlyCAg?= =?us-ascii?Q?OqC/UKXhUcIg3sKwuXTeC67eH2YYQ6AQhZDUUweLdv4k3Gwq6/usmEVYw7cW?= =?us-ascii?Q?4+o3hmwAO0khCyKRvcqYTT/sELhiBqEAd9EjrySi6TuoLhceE/8QGJ9LlkoY?= =?us-ascii?Q?j647x0yhMZ0D32KI7tEwTaJZsyIl9vLZfgvZ6mBB0h4sGu1IKUwXvEE+bzFF?= =?us-ascii?Q?N7rGFgdNcaLqWLjd2l2S/6AcfAsx2IHiwHHbTZB+gGSPntyonUme9U10F0Jq?= =?us-ascii?Q?HVQ9i6cyh320F61GkyBQGF178bm+P0hRF80WqqU8wlxwcEaa5XMy/ejbwFdv?= =?us-ascii?Q?dJ8jMsw/gcnBRTa1FsVr52x80GVWWFqr+liJbrAVSyqM94f8ll2MBA1ysEnj?= =?us-ascii?Q?LlC9coZVcyhpo5vgU5kldnYwDfG9lzku3Wh8bg4puYJ2+rojVmUJteg/Egdn?= =?us-ascii?Q?rN4mgWiWFRBBFrOwdXgwGXBQ0QrPLZTRquIVJm5UVA5FA7Xi8AgYJfw+dohp?= =?us-ascii?Q?Liu3GxqmHZ5q9Ye/BnH3gHrWh3wguroQNiSYdg+7qodvFXBnefyR9ogc8QxC?= =?us-ascii?Q?XmMUUznwbaByoRpl1/ta7/+5DdpWqU5TL8jYxvPYGDyRc9jr6x2DSD3Ydw5I?= =?us-ascii?Q?JVEmZ25UPk+aSkGs27n0Ji+Xn8vy/6KJv/ixuS+jikwx6tA7weSugYrEPuku?= =?us-ascii?Q?k/koE+g63CPD8smkydSy1CUD2tCm+edDkeTYvkg2itahrb9Bf23X1/Tptn+h?= =?us-ascii?Q?J9lbkTEaZ6/rdAWHYorzdmAUnYl/+lRm3XiZVZJBgfOmYzVu23So8SXUoNnp?= =?us-ascii?Q?cV68WlOPT1feHKANB5qC2Fv6USNDCoWxndEo7jhVpQubW8A+YlFp3hYa+VnR?= =?us-ascii?Q?0RGk2fcC83w6HOhqcy+4FFIs+JuL09NtKjHn7MeCQMvKs3rnlndTRQSPgSQZ?= =?us-ascii?Q?2HWRPagANLnrAVYBj0ZvWNeE7CgYVLARizgXhmniHMo4RYoZ+KMvqbLy+bVF?= =?us-ascii?Q?AZ1oCq9PzFOXDBtGck9h3n4ISSNLvGKblRbaxxY/sbcTd1ZDXu4rRBwFAZ0I?= =?us-ascii?Q?CxLOJgKmPCM7voord/ZV7jQ5prdadmtOxL/BOLtO4BHw9URClH2/w9I5YfuN?= =?us-ascii?Q?E+Wxo0Gmj26xxExup5mfVS0ZoL2/FYYfL+OaPBbru/FN9zXE+j10Y2YRZvBV?= =?us-ascii?Q?Z02APNY6FyhNud9OVai+1E8VjBddutSNFiNZrSN/GMLtT6O0A5H7jhLZFa9M?= =?us-ascii?Q?WbsUw82djUY71tllk1sNUuv6TSrbusDrk7jIZe4xO+LoJUa6tLRm5kY2mo2c?= =?us-ascii?Q?VVRKzQYw76S2kHdlcqwazCgNDoonT3ygTt047SXohN67gU8zMn79WSP/JwIa?= =?us-ascii?Q?HiblwgxMLCCqGic+kZ+MPlqBXtffWs0WyZhMTbYjfCdK+Gle8ejKodwXj7lB?= =?us-ascii?Q?itDQZxL26vkvVK2+iTEE3S+Lg+4ZhfubMbT7zG2w/GVFYERjL4VbalGDT5bp?= =?us-ascii?Q?Rpiij1nTj5/PeND2vBzALBTOusqJIBoZWcaphBOtsLFKm5y0DhohngJzPwcJ?= =?us-ascii?Q?JI00Z6t/fqqonDIHL91KIVe9xISSqYM/ZnqD0ePEXKw611GIYHK5W4lnWLt/?= =?us-ascii?Q?7DCdQ8tMEg=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 3a1d5726-74a7-4835-ac8c-08dea5f8a59d X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Apr 2026 14:07:28.4507 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: tcTtOjP3paVrcymd03ljmp+xeMNwueY4IcMtkLEqW4ofjilKbS0qYzhTfXDfVAJRTcMF4ri+wp2rb2eOc6I+6Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: LV8PR12MB9156 Hi Tejun, On Tue, Apr 28, 2026 at 10:35:36AM -1000, Tejun Heo wrote: > The auto-probed cid mapping reflects the kernel's view of topology > (node -> LLC -> core), but a BPF scheduler may want a different layout - > to align cid slices with its own partitioning, or to work around how the > kernel reports a particular machine. > > Add scx_bpf_cid_override(), callable from ops.init() of the root > scheduler. It validates the caller-supplied cpu->cid array and replaces > the in-place mapping; topo info is invalidated. A compat.bpf.h wrapper > silently no-ops on kernels that lack the kfunc. > > A new SCX_KF_ALLOW_INIT bit in the kfunc context filter restricts the > kfunc to ops.init() at verifier load time. > > Signed-off-by: Tejun Heo > Reviewed-by: Cheng-Yang Chou ... > +/** > + * scx_bpf_cid_override - Install an explicit cpu->cid mapping > + * @cpu_to_cid: array of nr_cpu_ids s32 entries (cid for each cpu) > + * @cpu_to_cid__sz: must be nr_cpu_ids * sizeof(s32) bytes > + * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs > + * > + * May only be called from ops.init() of the root scheduler. Replace the > + * topology-probed cid mapping with the caller-provided one. Each possible cpu > + * must map to a unique cid in [0, num_possible_cpus()). Topo info is cleared. > + * On invalid input, trigger scx_error() to abort the scheduler. > + */ > +__bpf_kfunc void scx_bpf_cid_override(const s32 *cpu_to_cid, u32 cpu_to_cid__sz, > + const struct bpf_prog_aux *aux) > +{ > + cpumask_var_t seen __free(free_cpumask_var) = CPUMASK_VAR_NULL; > + struct scx_sched *sch; > + bool alloced; > + s32 cpu, cid; > + > + /* GFP_KERNEL alloc must happen before the rcu read section */ > + alloced = zalloc_cpumask_var(&seen, GFP_KERNEL); > + > + guard(rcu)(); > + > + sch = scx_prog_sched(aux); > + if (unlikely(!sch)) > + return; > + > + if (!alloced) { > + scx_error(sch, "scx_bpf_cid_override: failed to allocate cpumask"); > + return; > + } > + > + if (scx_parent(sch)) { > + scx_error(sch, "scx_bpf_cid_override() only allowed from root sched"); > + return; > + } > + > + if (cpu_to_cid__sz != nr_cpu_ids * sizeof(s32)) { > + scx_error(sch, "scx_bpf_cid_override: expected %zu bytes, got %u", > + nr_cpu_ids * sizeof(s32), cpu_to_cid__sz); > + return; > + } > + > + for_each_possible_cpu(cpu) { > + s32 c = cpu_to_cid[cpu]; > + > + if (!cid_valid(sch, c)) > + return; > + if (cpumask_test_and_set_cpu(c, seen)) { > + scx_error(sch, "cid %d assigned to multiple cpus", c); > + return; > + } > + scx_cpu_to_cid_tbl[cpu] = c; > + scx_cid_to_cpu_tbl[c] = cpu; > + } > + > + /* Invalidate stale topo info - the override carries no topology. */ > + for (cid = 0; cid < num_possible_cpus(); cid++) > + scx_cid_topo[cid] = SCX_CID_TOPO_NEG; Considering that the topology info is wiped when scx_bpf_cid_override() is used, should we error if a scheduler is also trying to use scx_bpf_cid_topo() (i.e., setting a flag or similar)? Thanks, -Andrea