scx_flatcg: Use a user DSQ for fallback instead of SCX_DSQ_GLOBAL

scx_flatcg was using SCX_DSQ_GLOBAL for fallback handling. However, it is
assuming that SCX_DSQ_GLOBAL isn't automatically consumed, which was true a
while ago but is no longer the case. Also, there are further changes planned
for SCX_DSQ_GLOBAL which will disallow explicit consumption from it. Switch
to a user DSQ for fallback.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>

diff --git a/tools/sched_ext/scx_flatcg.bpf.c b/tools/sched_ext/scx_flatcg.bpf.c
index e272bc3..b722baf 100644 (file)
--- a/tools/sched_ext/scx_flatcg.bpf.c
+++ b/tools/sched_ext/scx_flatcg.bpf.c
@@ -49,7 +49,10 @@
 /*
  * Maximum amount of retries to find a valid cgroup.
  */
-#define CGROUP_MAX_RETRIES 1024
+enum {
+       FALLBACK_DSQ            = 0,
+       CGROUP_MAX_RETRIES      = 1024,
+};
 
 char _license[] SEC("license") = "GPL";
 
@@ -377,7 +380,7 @@ void BPF_STRUCT_OPS(fcg_enqueue, struct task_struct *p, u64 enq_flags)
                        scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, enq_flags);
                } else {
                        stat_inc(FCG_STAT_GLOBAL);
-                       scx_bpf_dispatch(p, SCX_DSQ_GLOBAL, SCX_SLICE_DFL, enq_flags);
+                       scx_bpf_dispatch(p, FALLBACK_DSQ, SCX_SLICE_DFL, enq_flags);
                }
                return;
        }
@@ -780,7 +783,7 @@ void BPF_STRUCT_OPS(fcg_dispatch, s32 cpu, struct task_struct *prev)
 pick_next_cgroup:
        cpuc->cur_at = now;
 
-       if (scx_bpf_consume(SCX_DSQ_GLOBAL)) {
+       if (scx_bpf_consume(FALLBACK_DSQ)) {
                cpuc->cur_cgid = 0;
                return;
        }
@@ -837,7 +840,7 @@ int BPF_STRUCT_OPS_SLEEPABLE(fcg_cgroup_init, struct cgroup *cgrp,
        int ret;
 
        /*
-        * Technically incorrect as cgroup ID is full 64bit while dq ID is
+        * Technically incorrect as cgroup ID is full 64bit while dsq ID is
         * 63bit. Should not be a problem in practice and easy to spot in the
         * unlikely case that it breaks.
         */
@@ -925,6 +928,11 @@ void BPF_STRUCT_OPS(fcg_cgroup_move, struct task_struct *p,
        p->scx.dsq_vtime = to_cgc->tvtime_now + vtime_delta;
 }
 
+s32 BPF_STRUCT_OPS_SLEEPABLE(fcg_init)
+{
+       return scx_bpf_create_dsq(FALLBACK_DSQ, -1);
+}
+
 void BPF_STRUCT_OPS(fcg_exit, struct scx_exit_info *ei)
 {
        UEI_RECORD(uei, ei);
@@ -943,6 +951,7 @@ SCX_OPS_DEFINE(flatcg_ops,
               .cgroup_init             = (void *)fcg_cgroup_init,
               .cgroup_exit             = (void *)fcg_cgroup_exit,
               .cgroup_move             = (void *)fcg_cgroup_move,
+              .init                    = (void *)fcg_init,
               .exit                    = (void *)fcg_exit,
               .flags                   = SCX_OPS_HAS_CGROUP_WEIGHT | SCX_OPS_ENQ_EXITING,
               .name                    = "flatcg");