/* 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 100/(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.
*
* The scheduler first picks the cgroup to run and then schedule the tasks
* within by using nested weighted vtime scheduling by default. The
* cgroup-internal scheduling can be switched to FIFO with the -f option.
*/
#include <scx/common.bpf.h>
#include "scx_flatcg.h"
/*
* Maximum amount of retries to find a valid cgroup.
*/
enum {
FALLBACK_DSQ = 0,
CGROUP_MAX_RETRIES = 1024,
};
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 fifo_sched;
u64 cvtime_now;
UEI_DEFINE(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 */
u64 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 opportunistic 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 = __sync_fetch_and_sub(&cgc->cvtime_delta, cgc->cvtime_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);
}
static void set_bypassed_at(struct task_struct *p, struct fcg_task_ctx *taskc)
{
/*
* 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;
}
s32 BPF_STRUCT_OPS(fcg_select_cpu, struct task_struct *p, s32 prev_cpu, u64 wake_flags)
{
struct fcg_task_ctx *taskc;
bool is_idle = false;
s32 cpu;
cpu = scx_bpf_select_cpu_dfl(p, prev_cpu, wake_flags, &is_idle);
taskc = bpf_task_storage_get(&task_ctx, p, 0, 0);
if (!taskc) {
scx_bpf_error("task_ctx lookup failed");
return cpu;
}
/*
* 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.
*/
if (is_idle) {
set_bypassed_at(p, taskc);
stat_inc(FCG_STAT_LOCAL);
scx_bpf_dispatch(p, SCX_DSQ_LOCAL, SCX_SLICE_DFL, 0);
}
return cpu;
}
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;
}
/*
* Use the direct dispatching and force charging 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 (p->nr_cpus_allowed != nr_cpus) {
set_bypassed_at(p, taskc);
/*
* 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 (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, FALLBACK_DSQ, SCX_SLICE_DFL, enq_flags);
}
return;
}
cgrp = __COMPAT_scx_bpf_task_cgroup(p);
cgc = find_cgrp_ctx(cgrp);
if (!cgc)
goto out_release;
if (fifo_sched) {
scx_bpf_dispatch(p, cgrp->kn->id, SCX_SLICE_DFL, enq_flags);
} else {
u64 tvtime = p->scx.dsq_vtime;
/*
* Limit the amount of budget that an idling task can accumulate
* to one slice.
*/
if (vtime_before(tvtime, cgc->tvtime_now - SCX_SLICE_DFL))
tvtime = cgc->tvtime_now - SCX_SLICE_DFL;
scx_bpf_dispatch_vtime(p, cgrp->kn->id, SCX_SLICE_DFL,
tvtime, 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 = __COMPAT_scx_bpf_task_cgroup(p);
update_active_weight_sums(cgrp, true);
bpf_cgroup_release(cgrp);
}
void BPF_STRUCT_OPS(fcg_running, struct task_struct *p)
{
struct cgroup *cgrp;
struct fcg_cgrp_ctx *cgc;
if (fifo_sched)
return;
cgrp = __COMPAT_scx_bpf_task_cgroup(p);
cgc = find_cgrp_ctx(cgrp);
if (cgc) {
/*
* @cgc->tvtime_now always progresses forward as tasks start
* executing. The test and update can be performed concurrently
* from multiple CPUs and thus racy. Any error should be
* contained and temporary. Let's just live with it.
*/
if (vtime_before(cgc->tvtime_now, p->scx.dsq_vtime))
cgc->tvtime_now = p->scx.dsq_vtime;
}
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;
/*
* Scale the execution time by the inverse of the weight and charge.
*
* Note that the default yield implementation yields by setting
* @p->scx.slice to zero and the following would treat the yielding task
* as if it has consumed all its slice. If this penalizes yielding tasks
* too much, determine the execution time by taking explicit timestamps
* instead of depending on @p->scx.slice.
*/
if (!fifo_sched)
p->scx.dsq_vtime +=
(SCX_SLICE_DFL - p->scx.slice) * 100 / p->scx.weight;
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 = __COMPAT_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 = __COMPAT_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);
stat_inc(FCG_STAT_PNC_RACE);
} 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();
bool picked_next = false;
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(FALLBACK_DSQ)) {
cpuc->cur_cgid = 0;
return;
}
bpf_repeat(CGROUP_MAX_RETRIES) {
if (try_pick_next_cgroup(&cpuc->cur_cgid)) {
picked_next = true;
break;
}
}
/*
* This only happens if try_pick_next_cgroup() races against enqueue
* path for more than CGROUP_MAX_RETRIES times, which is extremely
* unlikely and likely indicates an underlying bug. There shouldn't be
* any stall risk as the race is against enqueue.
*/
if (!picked_next)
stat_inc(FCG_STAT_PNC_FAIL);
}
s32 BPF_STRUCT_OPS(fcg_init_task, struct task_struct *p,
struct scx_init_task_args *args)
{
struct fcg_task_ctx *taskc;
struct fcg_cgrp_ctx *cgc;
/*
* @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;
if (!(cgc = find_cgrp_ctx(args->cgroup)))
return -ENOENT;
p->scx.dsq_vtime = cgc->tvtime_now;
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 dsq 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);
}
void BPF_STRUCT_OPS(fcg_cgroup_move, struct task_struct *p,
struct cgroup *from, struct cgroup *to)
{
struct fcg_cgrp_ctx *from_cgc, *to_cgc;
s64 vtime_delta;
/* find_cgrp_ctx() triggers scx_ops_error() on lookup failures */
if (!(from_cgc = find_cgrp_ctx(from)) || !(to_cgc = find_cgrp_ctx(to)))
return;
vtime_delta = p->scx.dsq_vtime - from_cgc->tvtime_now;
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);
}
SCX_OPS_DEFINE(flatcg_ops,
.select_cpu = (void *)fcg_select_cpu,
.enqueue = (void *)fcg_enqueue,
.dispatch = (void *)fcg_dispatch,
.runnable = (void *)fcg_runnable,
.running = (void *)fcg_running,
.stopping = (void *)fcg_stopping,
.quiescent = (void *)fcg_quiescent,
.init_task = (void *)fcg_init_task,
.cgroup_set_weight = (void *)fcg_cgroup_set_weight,
.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");
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