@@ -2,6 +2,7 @@ scx_simple
scx_qmap
scx_central
scx_pair
+scx_flatcg
*.skel.h
*.subskel.h
/tools/
@@ -179,7 +179,7 @@ SCX_COMMON_DEPS := scx_common.h user_exit_info.h | $(BINDIR)
################
# C schedulers #
################
-c-sched-targets = scx_simple scx_qmap scx_central scx_pair
+c-sched-targets = scx_simple scx_qmap scx_central scx_pair scx_flatcg
$(addprefix $(BINDIR)/,$(c-sched-targets)): \
$(BINDIR)/%: \
new file mode 100644
@@ -0,0 +1,834 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * A demo sched_ext flattened cgroup hierarchy scheduler. It implements
+ * hierarchical weight-based cgroup CPU control by flattening the cgroup
+ * hierarchy into a single layer by compounding the active weight share at each
+ * level. Consider the following hierarchy with weights in parentheses:
+ *
+ * R + A (100) + B (100)
+ * | \ C (100)
+ * \ D (200)
+ *
+ * Ignoring the root and threaded cgroups, only B, C and D can contain tasks.
+ * Let's say all three have runnable tasks. The total share that each of these
+ * three cgroups is entitled to can be calculated by compounding its share at
+ * each level.
+ *
+ * For example, B is competing against C and in that competition its share is
+ * 100/(100+100) == 1/2. At its parent level, A is competing against D and A's
+ * share in that competition is 200/(200+100) == 1/3. B's eventual share in the
+ * system can be calculated by multiplying the two shares, 1/2 * 1/3 == 1/6. C's
+ * eventual shaer is the same at 1/6. D is only competing at the top level and
+ * its share is 200/(100+200) == 2/3.
+ *
+ * So, instead of hierarchically scheduling level-by-level, we can consider it
+ * as B, C and D competing each other with respective share of 1/6, 1/6 and 2/3
+ * and keep updating the eventual shares as the cgroups' runnable states change.
+ *
+ * This flattening of hierarchy can bring a substantial performance gain when
+ * the cgroup hierarchy is nested multiple levels. in a simple benchmark using
+ * wrk[8] on apache serving a CGI script calculating sha1sum of a small file, it
+ * outperforms CFS by ~3% with CPU controller disabled and by ~10% with two
+ * apache instances competing with 2:1 weight ratio nested four level deep.
+ *
+ * However, the gain comes at the cost of not being able to properly handle
+ * thundering herd of cgroups. For example, if many cgroups which are nested
+ * behind a low priority parent cgroup wake up around the same time, they may be
+ * able to consume more CPU cycles than they are entitled to. In many use cases,
+ * this isn't a real concern especially given the performance gain. Also, there
+ * are ways to mitigate the problem further by e.g. introducing an extra
+ * scheduling layer on cgroup delegation boundaries.
+ */
+#include "scx_common.bpf.h"
+#include "user_exit_info.h"
+#include "scx_flatcg.h"
+
+char _license[] SEC("license") = "GPL";
+
+const volatile u32 nr_cpus = 32; /* !0 for veristat, set during init */
+const volatile u64 cgrp_slice_ns = SCX_SLICE_DFL;
+const volatile bool switch_partial;
+
+u64 cvtime_now;
+struct user_exit_info uei;
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __type(key, u32);
+ __type(value, u64);
+ __uint(max_entries, FCG_NR_STATS);
+} stats SEC(".maps");
+
+static void stat_inc(enum fcg_stat_idx idx)
+{
+ u32 idx_v = idx;
+
+ u64 *cnt_p = bpf_map_lookup_elem(&stats, &idx_v);
+ if (cnt_p)
+ (*cnt_p)++;
+}
+
+struct fcg_cpu_ctx {
+ u64 cur_cgid;
+ u64 cur_at;
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __type(key, u32);
+ __type(value, struct fcg_cpu_ctx);
+ __uint(max_entries, 1);
+} cpu_ctx SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_CGRP_STORAGE);
+ __uint(map_flags, BPF_F_NO_PREALLOC);
+ __type(key, int);
+ __type(value, struct fcg_cgrp_ctx);
+} cgrp_ctx SEC(".maps");
+
+struct cgv_node {
+ struct bpf_rb_node rb_node;
+ __u64 cvtime;
+ __u64 cgid;
+};
+
+private(CGV_TREE) struct bpf_spin_lock cgv_tree_lock;
+private(CGV_TREE) struct bpf_rb_root cgv_tree __contains(cgv_node, rb_node);
+
+struct cgv_node_stash {
+ struct cgv_node __kptr *node;
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 16384);
+ __type(key, __u64);
+ __type(value, struct cgv_node_stash);
+} cgv_node_stash SEC(".maps");
+
+struct fcg_task_ctx {
+ u64 bypassed_at;
+};
+
+struct {
+ __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+ __uint(map_flags, BPF_F_NO_PREALLOC);
+ __type(key, int);
+ __type(value, struct fcg_task_ctx);
+} task_ctx SEC(".maps");
+
+/* gets inc'd on weight tree changes to expire the cached hweights */
+unsigned long hweight_gen = 1;
+
+static u64 div_round_up(u64 dividend, u64 divisor)
+{
+ return (dividend + divisor - 1) / divisor;
+}
+
+static bool vtime_before(u64 a, u64 b)
+{
+ return (s64)(a - b) < 0;
+}
+
+static bool cgv_node_less(struct bpf_rb_node *a, const struct bpf_rb_node *b)
+{
+ struct cgv_node *cgc_a, *cgc_b;
+
+ cgc_a = container_of(a, struct cgv_node, rb_node);
+ cgc_b = container_of(b, struct cgv_node, rb_node);
+
+ return cgc_a->cvtime < cgc_b->cvtime;
+}
+
+static struct fcg_cpu_ctx *find_cpu_ctx(void)
+{
+ struct fcg_cpu_ctx *cpuc;
+ u32 idx = 0;
+
+ cpuc = bpf_map_lookup_elem(&cpu_ctx, &idx);
+ if (!cpuc) {
+ scx_bpf_error("cpu_ctx lookup failed");
+ return NULL;
+ }
+ return cpuc;
+}
+
+static struct fcg_cgrp_ctx *find_cgrp_ctx(struct cgroup *cgrp)
+{
+ struct fcg_cgrp_ctx *cgc;
+
+ cgc = bpf_cgrp_storage_get(&cgrp_ctx, cgrp, 0, 0);
+ if (!cgc) {
+ scx_bpf_error("cgrp_ctx lookup failed for cgid %llu", cgrp->kn->id);
+ return NULL;
+ }
+ return cgc;
+}
+
+static struct fcg_cgrp_ctx *find_ancestor_cgrp_ctx(struct cgroup *cgrp, int level)
+{
+ struct fcg_cgrp_ctx *cgc;
+
+ cgrp = bpf_cgroup_ancestor(cgrp, level);
+ if (!cgrp) {
+ scx_bpf_error("ancestor cgroup lookup failed");
+ return NULL;
+ }
+
+ cgc = find_cgrp_ctx(cgrp);
+ if (!cgc)
+ scx_bpf_error("ancestor cgrp_ctx lookup failed");
+ bpf_cgroup_release(cgrp);
+ return cgc;
+}
+
+static void cgrp_refresh_hweight(struct cgroup *cgrp, struct fcg_cgrp_ctx *cgc)
+{
+ int level;
+
+ if (!cgc->nr_active) {
+ stat_inc(FCG_STAT_HWT_SKIP);
+ return;
+ }
+
+ if (cgc->hweight_gen == hweight_gen) {
+ stat_inc(FCG_STAT_HWT_CACHE);
+ return;
+ }
+
+ stat_inc(FCG_STAT_HWT_UPDATES);
+ bpf_for(level, 0, cgrp->level + 1) {
+ struct fcg_cgrp_ctx *cgc;
+ bool is_active;
+
+ cgc = find_ancestor_cgrp_ctx(cgrp, level);
+ if (!cgc)
+ break;
+
+ if (!level) {
+ cgc->hweight = FCG_HWEIGHT_ONE;
+ cgc->hweight_gen = hweight_gen;
+ } else {
+ struct fcg_cgrp_ctx *pcgc;
+
+ pcgc = find_ancestor_cgrp_ctx(cgrp, level - 1);
+ if (!pcgc)
+ break;
+
+ /*
+ * We can be oppotunistic here and not grab the
+ * cgv_tree_lock and deal with the occasional races.
+ * However, hweight updates are already cached and
+ * relatively low-frequency. Let's just do the
+ * straightforward thing.
+ */
+ bpf_spin_lock(&cgv_tree_lock);
+ is_active = cgc->nr_active;
+ if (is_active) {
+ cgc->hweight_gen = pcgc->hweight_gen;
+ cgc->hweight =
+ div_round_up(pcgc->hweight * cgc->weight,
+ pcgc->child_weight_sum);
+ }
+ bpf_spin_unlock(&cgv_tree_lock);
+
+ if (!is_active) {
+ stat_inc(FCG_STAT_HWT_RACE);
+ break;
+ }
+ }
+ }
+}
+
+static void cgrp_cap_budget(struct cgv_node *cgv_node, struct fcg_cgrp_ctx *cgc)
+{
+ u64 delta, cvtime, max_budget;
+
+ /*
+ * A node which is on the rbtree can't be pointed to from elsewhere yet
+ * and thus can't be updated and repositioned. Instead, we collect the
+ * vtime deltas separately and apply it asynchronously here.
+ */
+ delta = cgc->cvtime_delta;
+ __sync_fetch_and_sub(&cgc->cvtime_delta, delta);
+ cvtime = cgv_node->cvtime + delta;
+
+ /*
+ * Allow a cgroup to carry the maximum budget proportional to its
+ * hweight such that a full-hweight cgroup can immediately take up half
+ * of the CPUs at the most while staying at the front of the rbtree.
+ */
+ max_budget = (cgrp_slice_ns * nr_cpus * cgc->hweight) /
+ (2 * FCG_HWEIGHT_ONE);
+ if (vtime_before(cvtime, cvtime_now - max_budget))
+ cvtime = cvtime_now - max_budget;
+
+ cgv_node->cvtime = cvtime;
+}
+
+static void cgrp_enqueued(struct cgroup *cgrp, struct fcg_cgrp_ctx *cgc)
+{
+ struct cgv_node_stash *stash;
+ struct cgv_node *cgv_node;
+ u64 cgid = cgrp->kn->id;
+
+ /* paired with cmpxchg in try_pick_next_cgroup() */
+ if (__sync_val_compare_and_swap(&cgc->queued, 0, 1)) {
+ stat_inc(FCG_STAT_ENQ_SKIP);
+ return;
+ }
+
+ stash = bpf_map_lookup_elem(&cgv_node_stash, &cgid);
+ if (!stash) {
+ scx_bpf_error("cgv_node lookup failed for cgid %llu", cgid);
+ return;
+ }
+
+ /* NULL if the node is already on the rbtree */
+ cgv_node = bpf_kptr_xchg(&stash->node, NULL);
+ if (!cgv_node) {
+ stat_inc(FCG_STAT_ENQ_RACE);
+ return;
+ }
+
+ bpf_spin_lock(&cgv_tree_lock);
+ cgrp_cap_budget(cgv_node, cgc);
+ bpf_rbtree_add(&cgv_tree, &cgv_node->rb_node, cgv_node_less);
+ bpf_spin_unlock(&cgv_tree_lock);
+}
+
+void BPF_STRUCT_OPS(fcg_enqueue, struct task_struct *p, u64 enq_flags)
+{
+ struct fcg_task_ctx *taskc;
+ struct cgroup *cgrp;
+ struct fcg_cgrp_ctx *cgc;
+
+ taskc = bpf_task_storage_get(&task_ctx, p, 0, 0);
+ if (!taskc) {
+ scx_bpf_error("task_ctx lookup failed");
+ return;
+ }
+
+ /*
+ * If select_cpu_dfl() is recommending local enqueue, the target CPU is
+ * idle. Follow it and charge the cgroup later in fcg_stopping() after
+ * the fact. Use the same mechanism to deal with tasks with custom
+ * affinities so that we don't have to worry about per-cgroup dq's
+ * containing tasks that can't be executed from some CPUs.
+ */
+ if ((enq_flags & SCX_ENQ_LOCAL) || p->nr_cpus_allowed != nr_cpus) {
+ /*
+ * Tell fcg_stopping() that this bypassed the regular scheduling
+ * path and should be force charged to the cgroup. 0 is used to
+ * indicate that the task isn't bypassing, so if the current
+ * runtime is 0, go back by one nanosecond.
+ */
+ taskc->bypassed_at = p->se.sum_exec_runtime ?: (u64)-1;
+
+ /*
+ * The global dq is deprioritized as we don't want to let tasks
+ * to boost themselves by constraining its cpumask. The
+ * deprioritization is rather severe, so let's not apply that to
+ * per-cpu kernel threads. This is ham-fisted. We probably wanna
+ * implement per-cgroup fallback dq's instead so that we have
+ * more control over when tasks with custom cpumask get issued.
+ */
+ if ((enq_flags & SCX_ENQ_LOCAL) ||
+ (p->nr_cpus_allowed == 1 && (p->flags & PF_KTHREAD))) {
+ stat_inc(FCG_STAT_LOCAL);
+ 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);
+ }
+ return;
+ }
+
+ cgrp = scx_bpf_task_cgroup(p);
+ cgc = find_cgrp_ctx(cgrp);
+ if (!cgc)
+ goto out_release;
+
+ scx_bpf_dispatch(p, cgrp->kn->id, SCX_SLICE_DFL, enq_flags);
+
+ cgrp_enqueued(cgrp, cgc);
+out_release:
+ bpf_cgroup_release(cgrp);
+}
+
+/*
+ * Walk the cgroup tree to update the active weight sums as tasks wake up and
+ * sleep. The weight sums are used as the base when calculating the proportion a
+ * given cgroup or task is entitled to at each level.
+ */
+static void update_active_weight_sums(struct cgroup *cgrp, bool runnable)
+{
+ struct fcg_cgrp_ctx *cgc;
+ bool updated = false;
+ int idx;
+
+ cgc = find_cgrp_ctx(cgrp);
+ if (!cgc)
+ return;
+
+ /*
+ * In most cases, a hot cgroup would have multiple threads going to
+ * sleep and waking up while the whole cgroup stays active. In leaf
+ * cgroups, ->nr_runnable which is updated with __sync operations gates
+ * ->nr_active updates, so that we don't have to grab the cgv_tree_lock
+ * repeatedly for a busy cgroup which is staying active.
+ */
+ if (runnable) {
+ if (__sync_fetch_and_add(&cgc->nr_runnable, 1))
+ return;
+ stat_inc(FCG_STAT_ACT);
+ } else {
+ if (__sync_sub_and_fetch(&cgc->nr_runnable, 1))
+ return;
+ stat_inc(FCG_STAT_DEACT);
+ }
+
+ /*
+ * If @cgrp is becoming runnable, its hweight should be refreshed after
+ * it's added to the weight tree so that enqueue has the up-to-date
+ * value. If @cgrp is becoming quiescent, the hweight should be
+ * refreshed before it's removed from the weight tree so that the usage
+ * charging which happens afterwards has access to the latest value.
+ */
+ if (!runnable)
+ cgrp_refresh_hweight(cgrp, cgc);
+
+ /* propagate upwards */
+ bpf_for(idx, 0, cgrp->level) {
+ int level = cgrp->level - idx;
+ struct fcg_cgrp_ctx *cgc, *pcgc = NULL;
+ bool propagate = false;
+
+ cgc = find_ancestor_cgrp_ctx(cgrp, level);
+ if (!cgc)
+ break;
+ if (level) {
+ pcgc = find_ancestor_cgrp_ctx(cgrp, level - 1);
+ if (!pcgc)
+ break;
+ }
+
+ /*
+ * We need the propagation protected by a lock to synchronize
+ * against weight changes. There's no reason to drop the lock at
+ * each level but bpf_spin_lock() doesn't want any function
+ * calls while locked.
+ */
+ bpf_spin_lock(&cgv_tree_lock);
+
+ if (runnable) {
+ if (!cgc->nr_active++) {
+ updated = true;
+ if (pcgc) {
+ propagate = true;
+ pcgc->child_weight_sum += cgc->weight;
+ }
+ }
+ } else {
+ if (!--cgc->nr_active) {
+ updated = true;
+ if (pcgc) {
+ propagate = true;
+ pcgc->child_weight_sum -= cgc->weight;
+ }
+ }
+ }
+
+ bpf_spin_unlock(&cgv_tree_lock);
+
+ if (!propagate)
+ break;
+ }
+
+ if (updated)
+ __sync_fetch_and_add(&hweight_gen, 1);
+
+ if (runnable)
+ cgrp_refresh_hweight(cgrp, cgc);
+}
+
+void BPF_STRUCT_OPS(fcg_runnable, struct task_struct *p, u64 enq_flags)
+{
+ struct cgroup *cgrp;
+
+ cgrp = scx_bpf_task_cgroup(p);
+ update_active_weight_sums(cgrp, true);
+ bpf_cgroup_release(cgrp);
+}
+
+void BPF_STRUCT_OPS(fcg_stopping, struct task_struct *p, bool runnable)
+{
+ struct fcg_task_ctx *taskc;
+ struct cgroup *cgrp;
+ struct fcg_cgrp_ctx *cgc;
+
+ taskc = bpf_task_storage_get(&task_ctx, p, 0, 0);
+ if (!taskc) {
+ scx_bpf_error("task_ctx lookup failed");
+ return;
+ }
+
+ if (!taskc->bypassed_at)
+ return;
+
+ cgrp = scx_bpf_task_cgroup(p);
+ cgc = find_cgrp_ctx(cgrp);
+ if (cgc) {
+ __sync_fetch_and_add(&cgc->cvtime_delta,
+ p->se.sum_exec_runtime - taskc->bypassed_at);
+ taskc->bypassed_at = 0;
+ }
+ bpf_cgroup_release(cgrp);
+}
+
+void BPF_STRUCT_OPS(fcg_quiescent, struct task_struct *p, u64 deq_flags)
+{
+ struct cgroup *cgrp;
+
+ cgrp = scx_bpf_task_cgroup(p);
+ update_active_weight_sums(cgrp, false);
+ bpf_cgroup_release(cgrp);
+}
+
+void BPF_STRUCT_OPS(fcg_cgroup_set_weight, struct cgroup *cgrp, u32 weight)
+{
+ struct fcg_cgrp_ctx *cgc, *pcgc = NULL;
+
+ cgc = find_cgrp_ctx(cgrp);
+ if (!cgc)
+ return;
+
+ if (cgrp->level) {
+ pcgc = find_ancestor_cgrp_ctx(cgrp, cgrp->level - 1);
+ if (!pcgc)
+ return;
+ }
+
+ bpf_spin_lock(&cgv_tree_lock);
+ if (pcgc && cgc->nr_active)
+ pcgc->child_weight_sum += (s64)weight - cgc->weight;
+ cgc->weight = weight;
+ bpf_spin_unlock(&cgv_tree_lock);
+}
+
+static bool try_pick_next_cgroup(u64 *cgidp)
+{
+ struct bpf_rb_node *rb_node;
+ struct cgv_node_stash *stash;
+ struct cgv_node *cgv_node;
+ struct fcg_cgrp_ctx *cgc;
+ struct cgroup *cgrp;
+ u64 cgid;
+
+ /* pop the front cgroup and wind cvtime_now accordingly */
+ bpf_spin_lock(&cgv_tree_lock);
+
+ rb_node = bpf_rbtree_first(&cgv_tree);
+ if (!rb_node) {
+ bpf_spin_unlock(&cgv_tree_lock);
+ stat_inc(FCG_STAT_PNC_NO_CGRP);
+ *cgidp = 0;
+ return true;
+ }
+
+ rb_node = bpf_rbtree_remove(&cgv_tree, rb_node);
+ bpf_spin_unlock(&cgv_tree_lock);
+
+ if (!rb_node) {
+ /*
+ * This should never happen. bpf_rbtree_first() was called
+ * above while the tree lock was held, so the node should
+ * always be present.
+ */
+ scx_bpf_error("node could not be removed");
+ return true;
+ }
+
+ cgv_node = container_of(rb_node, struct cgv_node, rb_node);
+ cgid = cgv_node->cgid;
+
+ if (vtime_before(cvtime_now, cgv_node->cvtime))
+ cvtime_now = cgv_node->cvtime;
+
+ /*
+ * If lookup fails, the cgroup's gone. Free and move on. See
+ * fcg_cgroup_exit().
+ */
+ cgrp = bpf_cgroup_from_id(cgid);
+ if (!cgrp) {
+ stat_inc(FCG_STAT_PNC_GONE);
+ goto out_free;
+ }
+
+ cgc = bpf_cgrp_storage_get(&cgrp_ctx, cgrp, 0, 0);
+ if (!cgc) {
+ bpf_cgroup_release(cgrp);
+ stat_inc(FCG_STAT_PNC_GONE);
+ goto out_free;
+ }
+
+ if (!scx_bpf_consume(cgid)) {
+ bpf_cgroup_release(cgrp);
+ stat_inc(FCG_STAT_PNC_EMPTY);
+ goto out_stash;
+ }
+
+ /*
+ * Successfully consumed from the cgroup. This will be our current
+ * cgroup for the new slice. Refresh its hweight.
+ */
+ cgrp_refresh_hweight(cgrp, cgc);
+
+ bpf_cgroup_release(cgrp);
+
+ /*
+ * As the cgroup may have more tasks, add it back to the rbtree. Note
+ * that here we charge the full slice upfront and then exact later
+ * according to the actual consumption. This prevents lowpri thundering
+ * herd from saturating the machine.
+ */
+ bpf_spin_lock(&cgv_tree_lock);
+ cgv_node->cvtime += cgrp_slice_ns * FCG_HWEIGHT_ONE / (cgc->hweight ?: 1);
+ cgrp_cap_budget(cgv_node, cgc);
+ bpf_rbtree_add(&cgv_tree, &cgv_node->rb_node, cgv_node_less);
+ bpf_spin_unlock(&cgv_tree_lock);
+
+ *cgidp = cgid;
+ stat_inc(FCG_STAT_PNC_NEXT);
+ return true;
+
+out_stash:
+ stash = bpf_map_lookup_elem(&cgv_node_stash, &cgid);
+ if (!stash) {
+ stat_inc(FCG_STAT_PNC_GONE);
+ goto out_free;
+ }
+
+ /*
+ * Paired with cmpxchg in cgrp_enqueued(). If they see the following
+ * transition, they'll enqueue the cgroup. If they are earlier, we'll
+ * see their task in the dq below and requeue the cgroup.
+ */
+ __sync_val_compare_and_swap(&cgc->queued, 1, 0);
+
+ if (scx_bpf_dsq_nr_queued(cgid)) {
+ bpf_spin_lock(&cgv_tree_lock);
+ bpf_rbtree_add(&cgv_tree, &cgv_node->rb_node, cgv_node_less);
+ bpf_spin_unlock(&cgv_tree_lock);
+ } else {
+ cgv_node = bpf_kptr_xchg(&stash->node, cgv_node);
+ if (cgv_node) {
+ scx_bpf_error("unexpected !NULL cgv_node stash");
+ goto out_free;
+ }
+ }
+
+ return false;
+
+out_free:
+ bpf_obj_drop(cgv_node);
+ return false;
+}
+
+void BPF_STRUCT_OPS(fcg_dispatch, s32 cpu, struct task_struct *prev)
+{
+ struct fcg_cpu_ctx *cpuc;
+ struct fcg_cgrp_ctx *cgc;
+ struct cgroup *cgrp;
+ u64 now = bpf_ktime_get_ns();
+
+ cpuc = find_cpu_ctx();
+ if (!cpuc)
+ return;
+
+ if (!cpuc->cur_cgid)
+ goto pick_next_cgroup;
+
+ if (vtime_before(now, cpuc->cur_at + cgrp_slice_ns)) {
+ if (scx_bpf_consume(cpuc->cur_cgid)) {
+ stat_inc(FCG_STAT_CNS_KEEP);
+ return;
+ }
+ stat_inc(FCG_STAT_CNS_EMPTY);
+ } else {
+ stat_inc(FCG_STAT_CNS_EXPIRE);
+ }
+
+ /*
+ * The current cgroup is expiring. It was already charged a full slice.
+ * Calculate the actual usage and accumulate the delta.
+ */
+ cgrp = bpf_cgroup_from_id(cpuc->cur_cgid);
+ if (!cgrp) {
+ stat_inc(FCG_STAT_CNS_GONE);
+ goto pick_next_cgroup;
+ }
+
+ cgc = bpf_cgrp_storage_get(&cgrp_ctx, cgrp, 0, 0);
+ if (cgc) {
+ /*
+ * We want to update the vtime delta and then look for the next
+ * cgroup to execute but the latter needs to be done in a loop
+ * and we can't keep the lock held. Oh well...
+ */
+ bpf_spin_lock(&cgv_tree_lock);
+ __sync_fetch_and_add(&cgc->cvtime_delta,
+ (cpuc->cur_at + cgrp_slice_ns - now) *
+ FCG_HWEIGHT_ONE / (cgc->hweight ?: 1));
+ bpf_spin_unlock(&cgv_tree_lock);
+ } else {
+ stat_inc(FCG_STAT_CNS_GONE);
+ }
+
+ bpf_cgroup_release(cgrp);
+
+pick_next_cgroup:
+ cpuc->cur_at = now;
+
+ if (scx_bpf_consume(SCX_DSQ_GLOBAL)) {
+ cpuc->cur_cgid = 0;
+ return;
+ }
+
+ bpf_repeat(BPF_MAX_LOOPS) {
+ if (try_pick_next_cgroup(&cpuc->cur_cgid))
+ break;
+ }
+}
+
+s32 BPF_STRUCT_OPS(fcg_prep_enable, struct task_struct *p,
+ struct scx_enable_args *args)
+{
+ struct fcg_task_ctx *taskc;
+
+ /*
+ * @p is new. Let's ensure that its task_ctx is available. We can sleep
+ * in this function and the following will automatically use GFP_KERNEL.
+ */
+ taskc = bpf_task_storage_get(&task_ctx, p, 0,
+ BPF_LOCAL_STORAGE_GET_F_CREATE);
+ if (!taskc)
+ return -ENOMEM;
+
+ taskc->bypassed_at = 0;
+ return 0;
+}
+
+int BPF_STRUCT_OPS_SLEEPABLE(fcg_cgroup_init, struct cgroup *cgrp,
+ struct scx_cgroup_init_args *args)
+{
+ struct fcg_cgrp_ctx *cgc;
+ struct cgv_node *cgv_node;
+ struct cgv_node_stash empty_stash = {}, *stash;
+ u64 cgid = cgrp->kn->id;
+ int ret;
+
+ /*
+ * Technically incorrect as cgroup ID is full 64bit while dq ID is
+ * 63bit. Should not be a problem in practice and easy to spot in the
+ * unlikely case that it breaks.
+ */
+ ret = scx_bpf_create_dsq(cgid, -1);
+ if (ret)
+ return ret;
+
+ cgc = bpf_cgrp_storage_get(&cgrp_ctx, cgrp, 0,
+ BPF_LOCAL_STORAGE_GET_F_CREATE);
+ if (!cgc) {
+ ret = -ENOMEM;
+ goto err_destroy_dsq;
+ }
+
+ cgc->weight = args->weight;
+ cgc->hweight = FCG_HWEIGHT_ONE;
+
+ ret = bpf_map_update_elem(&cgv_node_stash, &cgid, &empty_stash,
+ BPF_NOEXIST);
+ if (ret) {
+ if (ret != -ENOMEM)
+ scx_bpf_error("unexpected stash creation error (%d)",
+ ret);
+ goto err_destroy_dsq;
+ }
+
+ stash = bpf_map_lookup_elem(&cgv_node_stash, &cgid);
+ if (!stash) {
+ scx_bpf_error("unexpected cgv_node stash lookup failure");
+ ret = -ENOENT;
+ goto err_destroy_dsq;
+ }
+
+ cgv_node = bpf_obj_new(struct cgv_node);
+ if (!cgv_node) {
+ ret = -ENOMEM;
+ goto err_del_cgv_node;
+ }
+
+ cgv_node->cgid = cgid;
+ cgv_node->cvtime = cvtime_now;
+
+ cgv_node = bpf_kptr_xchg(&stash->node, cgv_node);
+ if (cgv_node) {
+ scx_bpf_error("unexpected !NULL cgv_node stash");
+ ret = -EBUSY;
+ goto err_drop;
+ }
+
+ return 0;
+
+err_drop:
+ bpf_obj_drop(cgv_node);
+err_del_cgv_node:
+ bpf_map_delete_elem(&cgv_node_stash, &cgid);
+err_destroy_dsq:
+ scx_bpf_destroy_dsq(cgid);
+ return ret;
+}
+
+void BPF_STRUCT_OPS(fcg_cgroup_exit, struct cgroup *cgrp)
+{
+ u64 cgid = cgrp->kn->id;
+
+ /*
+ * For now, there's no way find and remove the cgv_node if it's on the
+ * cgv_tree. Let's drain them in the dispatch path as they get popped
+ * off the front of the tree.
+ */
+ bpf_map_delete_elem(&cgv_node_stash, &cgid);
+ scx_bpf_destroy_dsq(cgid);
+}
+
+s32 BPF_STRUCT_OPS(fcg_init)
+{
+ if (!switch_partial)
+ scx_bpf_switch_all();
+ return 0;
+}
+
+void BPF_STRUCT_OPS(fcg_exit, struct scx_exit_info *ei)
+{
+ uei_record(&uei, ei);
+}
+
+SEC(".struct_ops.link")
+struct sched_ext_ops flatcg_ops = {
+ .enqueue = (void *)fcg_enqueue,
+ .dispatch = (void *)fcg_dispatch,
+ .runnable = (void *)fcg_runnable,
+ .stopping = (void *)fcg_stopping,
+ .quiescent = (void *)fcg_quiescent,
+ .prep_enable = (void *)fcg_prep_enable,
+ .cgroup_set_weight = (void *)fcg_cgroup_set_weight,
+ .cgroup_init = (void *)fcg_cgroup_init,
+ .cgroup_exit = (void *)fcg_cgroup_exit,
+ .init = (void *)fcg_init,
+ .exit = (void *)fcg_exit,
+ .flags = SCX_OPS_CGROUP_KNOB_WEIGHT | SCX_OPS_ENQ_EXITING,
+ .name = "flatcg",
+};
new file mode 100644
@@ -0,0 +1,217 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2023 Meta Platforms, Inc. and affiliates.
+ * Copyright (c) 2023 Tejun Heo <tj@kernel.org>
+ * Copyright (c) 2023 David Vernet <dvernet@meta.com>
+ */
+#include <stdio.h>
+#include <signal.h>
+#include <unistd.h>
+#include <libgen.h>
+#include <limits.h>
+#include <fcntl.h>
+#include <time.h>
+#include <bpf/bpf.h>
+#include "scx_common.h"
+#include "scx_flatcg.h"
+#include "scx_flatcg.skel.h"
+
+#ifndef FILEID_KERNFS
+#define FILEID_KERNFS 0xfe
+#endif
+
+const char help_fmt[] =
+"A flattened cgroup hierarchy sched_ext scheduler.\n"
+"\n"
+"See the top-level comment in .bpf.c for more details.\n"
+"\n"
+"Usage: %s [-s SLICE_US] [-i INTERVAL] [-p]\n"
+"\n"
+" -s SLICE_US Override slice duration\n"
+" -i INTERVAL Report interval\n"
+" -p Switch only tasks on SCHED_EXT policy intead of all\n"
+" -h Display this help and exit\n";
+
+static volatile int exit_req;
+
+static void sigint_handler(int dummy)
+{
+ exit_req = 1;
+}
+
+static float read_cpu_util(__u64 *last_sum, __u64 *last_idle)
+{
+ FILE *fp;
+ char buf[4096];
+ char *line, *cur = NULL, *tok;
+ __u64 sum = 0, idle = 0;
+ __u64 delta_sum, delta_idle;
+ int idx;
+
+ fp = fopen("/proc/stat", "r");
+ if (!fp) {
+ perror("fopen(\"/proc/stat\")");
+ return 0.0;
+ }
+
+ if (!fgets(buf, sizeof(buf), fp)) {
+ perror("fgets(\"/proc/stat\")");
+ fclose(fp);
+ return 0.0;
+ }
+ fclose(fp);
+
+ line = buf;
+ for (idx = 0; (tok = strtok_r(line, " \n", &cur)); idx++) {
+ char *endp = NULL;
+ __u64 v;
+
+ if (idx == 0) {
+ line = NULL;
+ continue;
+ }
+ v = strtoull(tok, &endp, 0);
+ if (!endp || *endp != '\0') {
+ fprintf(stderr, "failed to parse %dth field of /proc/stat (\"%s\")\n",
+ idx, tok);
+ continue;
+ }
+ sum += v;
+ if (idx == 4)
+ idle = v;
+ }
+
+ delta_sum = sum - *last_sum;
+ delta_idle = idle - *last_idle;
+ *last_sum = sum;
+ *last_idle = idle;
+
+ return delta_sum ? (float)(delta_sum - delta_idle) / delta_sum : 0.0;
+}
+
+static void fcg_read_stats(struct scx_flatcg *skel, __u64 *stats)
+{
+ __u64 cnts[FCG_NR_STATS][skel->rodata->nr_cpus];
+ __u32 idx;
+
+ memset(stats, 0, sizeof(stats[0]) * FCG_NR_STATS);
+
+ for (idx = 0; idx < FCG_NR_STATS; idx++) {
+ int ret, cpu;
+
+ ret = bpf_map_lookup_elem(bpf_map__fd(skel->maps.stats),
+ &idx, cnts[idx]);
+ if (ret < 0)
+ continue;
+ for (cpu = 0; cpu < skel->rodata->nr_cpus; cpu++)
+ stats[idx] += cnts[idx][cpu];
+ }
+}
+
+int main(int argc, char **argv)
+{
+ struct scx_flatcg *skel;
+ struct bpf_link *link;
+ struct timespec intv_ts = { .tv_sec = 2, .tv_nsec = 0 };
+ bool dump_cgrps = false;
+ __u64 last_cpu_sum = 0, last_cpu_idle = 0;
+ __u64 last_stats[FCG_NR_STATS] = {};
+ unsigned long seq = 0;
+ __s32 opt;
+
+ signal(SIGINT, sigint_handler);
+ signal(SIGTERM, sigint_handler);
+
+ libbpf_set_strict_mode(LIBBPF_STRICT_ALL);
+
+ skel = scx_flatcg__open();
+ SCX_BUG_ON(!skel, "Failed to open skel");
+
+ skel->rodata->nr_cpus = libbpf_num_possible_cpus();
+
+ while ((opt = getopt(argc, argv, "s:i:dfph")) != -1) {
+ double v;
+
+ switch (opt) {
+ case 's':
+ v = strtod(optarg, NULL);
+ skel->rodata->cgrp_slice_ns = v * 1000;
+ break;
+ case 'i':
+ v = strtod(optarg, NULL);
+ intv_ts.tv_sec = v;
+ intv_ts.tv_nsec = (v - (float)intv_ts.tv_sec) * 1000000000;
+ break;
+ case 'd':
+ dump_cgrps = true;
+ break;
+ case 'p':
+ skel->rodata->switch_partial = true;
+ break;
+ case 'h':
+ default:
+ fprintf(stderr, help_fmt, basename(argv[0]));
+ return opt != 'h';
+ }
+ }
+
+ printf("slice=%.1lfms intv=%.1lfs dump_cgrps=%d",
+ (double)skel->rodata->cgrp_slice_ns / 1000000.0,
+ (double)intv_ts.tv_sec + (double)intv_ts.tv_nsec / 1000000000.0,
+ dump_cgrps);
+
+ SCX_BUG_ON(scx_flatcg__load(skel), "Failed to load skel");
+
+ link = bpf_map__attach_struct_ops(skel->maps.flatcg_ops);
+ SCX_BUG_ON(!link, "Failed to attach struct_ops");
+
+ while (!exit_req && !uei_exited(&skel->bss->uei)) {
+ __u64 acc_stats[FCG_NR_STATS];
+ __u64 stats[FCG_NR_STATS];
+ float cpu_util;
+ int i;
+
+ cpu_util = read_cpu_util(&last_cpu_sum, &last_cpu_idle);
+
+ fcg_read_stats(skel, acc_stats);
+ for (i = 0; i < FCG_NR_STATS; i++)
+ stats[i] = acc_stats[i] - last_stats[i];
+
+ memcpy(last_stats, acc_stats, sizeof(acc_stats));
+
+ printf("\n[SEQ %6lu cpu=%5.1lf hweight_gen=%lu]\n",
+ seq++, cpu_util * 100.0, skel->data->hweight_gen);
+ printf(" act:%6llu deact:%6llu local:%6llu global:%6llu\n",
+ stats[FCG_STAT_ACT],
+ stats[FCG_STAT_DEACT],
+ stats[FCG_STAT_LOCAL],
+ stats[FCG_STAT_GLOBAL]);
+ printf("HWT skip:%6llu race:%6llu cache:%6llu update:%6llu\n",
+ stats[FCG_STAT_HWT_SKIP],
+ stats[FCG_STAT_HWT_RACE],
+ stats[FCG_STAT_HWT_CACHE],
+ stats[FCG_STAT_HWT_UPDATES]);
+ printf("ENQ skip:%6llu race:%6llu\n",
+ stats[FCG_STAT_ENQ_SKIP],
+ stats[FCG_STAT_ENQ_RACE]);
+ printf("CNS keep:%6llu expire:%6llu empty:%6llu gone:%6llu\n",
+ stats[FCG_STAT_CNS_KEEP],
+ stats[FCG_STAT_CNS_EXPIRE],
+ stats[FCG_STAT_CNS_EMPTY],
+ stats[FCG_STAT_CNS_GONE]);
+ printf("PNC nocgrp:%6llu next:%6llu empty:%6llu gone:%6llu\n",
+ stats[FCG_STAT_PNC_NO_CGRP],
+ stats[FCG_STAT_PNC_NEXT],
+ stats[FCG_STAT_PNC_EMPTY],
+ stats[FCG_STAT_PNC_GONE]);
+ printf("BAD remove:%6llu\n",
+ acc_stats[FCG_STAT_BAD_REMOVAL]);
+
+ nanosleep(&intv_ts, NULL);
+ }
+
+ bpf_link__destroy(link);
+ uei_print(&skel->bss->uei);
+ scx_flatcg__destroy(skel);
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,49 @@
+#ifndef __SCX_EXAMPLE_FLATCG_H
+#define __SCX_EXAMPLE_FLATCG_H
+
+enum {
+ FCG_HWEIGHT_ONE = 1LLU << 16,
+};
+
+enum fcg_stat_idx {
+ FCG_STAT_ACT,
+ FCG_STAT_DEACT,
+ FCG_STAT_LOCAL,
+ FCG_STAT_GLOBAL,
+
+ FCG_STAT_HWT_UPDATES,
+ FCG_STAT_HWT_CACHE,
+ FCG_STAT_HWT_SKIP,
+ FCG_STAT_HWT_RACE,
+
+ FCG_STAT_ENQ_SKIP,
+ FCG_STAT_ENQ_RACE,
+
+ FCG_STAT_CNS_KEEP,
+ FCG_STAT_CNS_EXPIRE,
+ FCG_STAT_CNS_EMPTY,
+ FCG_STAT_CNS_GONE,
+
+ FCG_STAT_PNC_NO_CGRP,
+ FCG_STAT_PNC_NEXT,
+ FCG_STAT_PNC_EMPTY,
+ FCG_STAT_PNC_GONE,
+
+ FCG_STAT_BAD_REMOVAL,
+
+ FCG_NR_STATS,
+};
+
+struct fcg_cgrp_ctx {
+ u32 nr_active;
+ u32 nr_runnable;
+ u32 queued;
+ u32 weight;
+ u32 hweight;
+ u64 child_weight_sum;
+ u64 hweight_gen;
+ s64 cvtime_delta;
+ u64 tvtime_now;
+};
+
+#endif /* __SCX_EXAMPLE_FLATCG_H */