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scx_lavd: add missing reset_lock_futex_boost()

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reset_lock_futex_boost() should be called every context switch of a
task. Otherwise, in the worst case, a task and that CPU could block
the preemption. To avoid such a situation, add missing
reset_lock_futex_boost() calls.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
This commit is contained in:
Changwoo Min 2024-10-18 11:29:08 +09:00
parent b01ff79080
commit 8d63024be7
4 changed files with 45 additions and 25 deletions
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5
scheds/rust/scx_lavd/src/bpf/intf.h
View File

@ -132,9 +132,10 @@ struct task_ctx {
u32 lat_cri_waker; /* waker's latency criticality */
volatile s32 victim_cpu;
u16 slice_boost_prio; /* how many times a task fully consumed the slice */
u8 wakeup_ft; /* regular wakeup = 1, sync wakeup = 2 */
volatile s16 lock_boost; /* lock boost count */
volatile s16 futex_boost; /* futex boost count */
volatile u8 need_lock_boost; /* need to boost lock for deadline calculation */
u8 wakeup_ft; /* regular wakeup = 1, sync wakeup = 2 */
volatile u32 *futex_uaddr; /* futex uaddr */
/*
@ -176,7 +177,7 @@ enum {
};
enum {
LAVD_MSG_TASKC = 0x1,
LAVD_MSG_TASKC = 0x1
};
struct introspec {

8
scheds/rust/scx_lavd/src/bpf/lock.bpf.c
View File

@ -93,11 +93,17 @@ static void dec_futex_boost(u32 *uaddr)
try_dec_futex_boost(taskc, cpuc, uaddr);
}
static void reset_lock_futex_boost(struct task_ctx *taskc)
static void reset_lock_futex_boost(struct task_ctx *taskc, struct cpu_ctx *cpuc)
{
if (is_lock_holder(taskc)) {
taskc->need_lock_boost = true;
cpuc->nr_lhp++;
}
taskc->lock_boost = 0;
taskc->futex_boost = 0;
taskc->futex_uaddr = NULL;
cpuc->lock_holder = false;
}
/**

54
scheds/rust/scx_lavd/src/bpf/main.bpf.c
View File

@ -307,22 +307,18 @@ static u64 calc_lat_cri(struct task_struct *p, struct task_ctx *taskc,
if (is_kernel_task(p))
lat_cri += LAVD_LC_KTHREAD_FT;
/*
* Reset task's lock and futex boost count
* for a lock holder to be boosted only once.
*/
reset_lock_futex_boost(taskc, cpuc_cur);
/*
* Prioritize a lock holder for faster system-wide forward progress.
*/
if (is_lock_holder(taskc)) {
if (taskc->need_lock_boost) {
taskc->need_lock_boost = false;
lat_cri += (lat_cri * LAVD_LC_LOCK_HOLDER_FT) / 1000;
/*
* Update statistics.
*/
cpuc_cur->nr_lhp++;
/*
* Reset task's lock and futex boost count
* for a lock holder to be boosted only once.
*/
reset_lock_futex_boost(taskc);
}
/*
@ -363,7 +359,9 @@ static u64 calc_task_load_actual(struct task_ctx *taskc)
* can be calculated from task's average run time and frequency.
*/
const s64 interval_adj = LAVD_TIME_ONE_SEC / LAVD_SYS_STAT_INTERVAL_NS;
return (taskc->run_time_ns * taskc->run_freq) / interval_adj;
u64 load = (taskc->run_time_ns * taskc->run_freq) / interval_adj;
return min(load, LAVD_TIME_ONE_SEC);
}
static u64 clamp_time_slice_ns(u64 slice)
@ -629,6 +627,12 @@ static void update_stat_for_stopping(struct task_struct *p,
*/
if (READ_ONCE(cur_svc_time) < taskc->svc_time)
WRITE_ONCE(cur_svc_time, taskc->svc_time);
/*
* Reset task's lock and futex boost count
* for a lock holder to be boosted only once.
*/
reset_lock_futex_boost(taskc, cpuc);
}
static void update_stat_for_quiescent(struct task_struct *p,
@ -641,6 +645,12 @@ static void update_stat_for_quiescent(struct task_struct *p,
*/
cpuc->load_actual -= taskc->load_actual;
cpuc->load_run_time_ns -= clamp_time_slice_ns(taskc->run_time_ns);
/*
* Reset task's lock and futex boost count
* for a lock holder to be boosted only once.
*/
reset_lock_futex_boost(taskc, cpuc);
}
static bool match_task_core_type(struct task_ctx *taskc,
@ -1174,8 +1184,7 @@ void BPF_STRUCT_OPS(lavd_dispatch, s32 cpu, struct task_struct *prev)
u64 now = bpf_ktime_get_ns();
struct cpu_ctx *cpuc;
struct bpf_cpumask *active, *ovrflw;
struct task_struct *p;
struct task_ctx *taskc;
struct task_struct *p, *taskc;
u64 dsq_id = 0;
bool try_consume = false;
@ -1289,20 +1298,27 @@ consume_out:
*/
if (!try_consume)
return;
if (consume_task(cpu, cpuc, now))
return;
/*
* If no other task is consumed, the scheduler will keep continue to
* run the prev task, so let's re-assigne its time slice.
* Reset prev task's lock and futex boost count
* for a lock holder to be boosted only once.
*/
if (prev && (prev->scx.flags & SCX_TASK_QUEUED)) {
if (prev) {
taskc = get_task_ctx(prev);
if (!taskc) {
scx_bpf_error("Failed to look up task context");
return;
}
prev->scx.slice = calc_time_slice(prev, taskc);
reset_lock_futex_boost(taskc, cpuc);
/*
* If nothing to run, continue to run the previous task.
*/
if (prev->scx.flags & SCX_TASK_QUEUED)
prev->scx.slice = calc_time_slice(prev, taskc);
}
}

3
scripts/dsq_lat.bt
View File

@ -51,9 +51,6 @@ rawtracepoint:sched_switch
}
interval:s:1 {
$scx_ops = kaddr("scx_ops");
$ops = (struct sched_ext_ops*)$scx_ops;
printf("scheduler: %s\n", $ops->name);
print(@avg_lat);
print(@usec_hist);
print(@dsq_lat);