[PATCH] sched_ext/scx_flatcg: expire cached hweights on weight changes
Tao Cui <[email protected]>
| Newsgroups | dev.linux.lists.sched-ext,org.kernel.vger.bpf,org.kernel.vger.linux-kernel |
|---|---|
| Message-ID | <[email protected]> |
From: Tao Cui <[email protected]> fcg_cgroup_set_weight() updates cgc->weight and the parent's child_weight_sum but doesn't bump hweight_gen, so the hweights cached by cgrp_refresh_hweight() stay stale until some task activation bumps the generation. For cgroups whose tasks never go through a 0->n runnable transition (e.g. persistently busy ones), a cpu.weight change never propagates to scheduling at all. Bump hweight_gen on weight changes so the next refresh recomputes with the new weight. Verified on a flatcg VM: a live cpu.weight 100->800 change on a busy cgroup leaves HWT update at 0 and the distribution unchanged; with it, hweight_gen increments and the refresh recomputes. Signed-off-by: Tao Cui <[email protected]> --- tools/sched_ext/scx_flatcg.bpf.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c index 0fd214cc61da..2d178c2ecacc 100644 --- a/tools/sched_ext/scx_flatcg.bpf.c +++ b/tools/sched_ext/scx_flatcg.bpf.c @@ -605,6 +605,9 @@ void BPF_STRUCT_OPS(fcg_cgroup_set_weight, struct cgroup *cgrp, u32 weight) pcgc->child_weight_sum += (s64)weight - cgc->weight; cgc->weight = weight; bpf_spin_unlock(&cgv_tree_lock); + + /* expire cached hweights so the new weight propagates */ + __sync_fetch_and_add(&hweight_gen, 1); } static bool try_pick_next_cgroup(u64 *cgidp) -- 2.43.0