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MEDIUM: tasks: implement 3 different tasklet classes with their own queues

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We used to mix high latency tasks and low latency tasklets in the same
list, and to even refill bulk tasklets there, causing some unfairness
in certain situations (e.g. poll-less transfers between many connections
saturating the machine with similarly-sized in and out network interfaces).

This patch changes the mechanism to split the load into 3 lists depending
on the task/tasklet's desired classes :
  - URGENT: this is mainly for tasklets used as deferred callbacks
  - NORMAL: this is for regular tasks
  - BULK: this is for bulk tasks/tasklets

Arbitrary ratios of max_processed are picked from each of these lists in
turn, with the ability to complete in one list from what was not picked
in the previous one. After some quick tests, the following setup gave
apparently good results both for raw TCP with splicing and for H2-to-H1
request rate:

  - 0 to 75% for urgent
  - 12 to 50% for normal
  - 12 to what remains for bulk

Bulk is not used yet.
This commit is contained in:
Willy Tarreau 2020-01-30 18:37:28 +01:00
parent 4ffa0b526a
commit a62917b890
4 changed files with 41 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/proto/task.h
View File

@ -245,7 +245,7 @@ static inline void tasklet_wakeup(struct tasklet *tl)
if (likely(tl->tid < 0)) {
/* this tasklet runs on the caller thread */
if (LIST_ISEMPTY(&tl->list)) {
LIST_ADDQ(&task_per_thread[tid].task_list, &tl->list);
LIST_ADDQ(&task_per_thread[tid].tasklets[TL_URGENT], &tl->list);
_HA_ATOMIC_ADD(&tasks_run_queue, 1);
}
} else {
@ -264,10 +264,10 @@ static inline void tasklet_wakeup(struct tasklet *tl)
/* Insert a tasklet into the tasklet list. If used with a plain task instead,
* the caller must update the task_list_size.
*/
static inline void tasklet_insert_into_tasklet_list(struct tasklet *tl)
static inline void tasklet_insert_into_tasklet_list(struct list *list, struct tasklet *tl)
{
_HA_ATOMIC_ADD(&tasks_run_queue, 1);
LIST_ADDQ(&sched->task_list, &tl->list);
LIST_ADDQ(list, &tl->list);
}
/* Remove the tasklet from the tasklet list. The tasklet MUST already be there.
@ -581,7 +581,10 @@ static inline int thread_has_tasks(void)
{
return (!!(global_tasks_mask & tid_bit) |
(sched->rqueue_size > 0) |
!LIST_ISEMPTY(&sched->task_list) | !MT_LIST_ISEMPTY(&sched->shared_tasklet_list));
!LIST_ISEMPTY(&sched->tasklets[TL_URGENT]) |
!LIST_ISEMPTY(&sched->tasklets[TL_NORMAL]) |
!LIST_ISEMPTY(&sched->tasklets[TL_BULK]) |
!MT_LIST_ISEMPTY(&sched->shared_tasklet_list));
}
/* adds list item <item> to work list <work> and wake up the associated task */

11
include/types/task.h
View File

@ -50,6 +50,13 @@
TASK_WOKEN_IO|TASK_WOKEN_SIGNAL|TASK_WOKEN_MSG| \
TASK_WOKEN_RES)
enum {
TL_URGENT = 0, /* urgent tasklets (I/O callbacks) */
TL_NORMAL = 1, /* normal tasks */
TL_BULK = 2, /* bulk task/tasklets, streaming I/Os */
TL_CLASSES /* must be last */
};
struct notification {
struct list purge_me; /* Part of the list of signals to be purged in the
case of the LUA execution stack crash. */
@ -63,9 +70,9 @@ struct notification {
struct task_per_thread {
struct eb_root timers; /* tree constituting the per-thread wait queue */
struct eb_root rqueue; /* tree constituting the per-thread run queue */
struct list task_list; /* List of tasks to be run, mixing tasks and tasklets */
struct mt_list shared_tasklet_list; /* Tasklet to be run, woken up by other threads */
int task_list_size; /* Number of tasks in the task_list */
struct list tasklets[TL_CLASSES]; /* tasklets (and/or tasks) to run, by class */
int task_list_size; /* Number of tasks among the tasklets */
int rqueue_size; /* Number of elements in the per-thread run queue */
struct task *current; /* current task (not tasklet) */
__attribute__((aligned(64))) char end[0];

6
src/debug.c
View File

@ -63,8 +63,10 @@ void ha_thread_dump(struct buffer *buf, int thr, int calling_tid)
!!(global_tasks_mask & thr_bit),
!eb_is_empty(&task_per_thread[thr].timers),
!eb_is_empty(&task_per_thread[thr].rqueue),
!(LIST_ISEMPTY(&task_per_thread[thr].task_list) |
MT_LIST_ISEMPTY(&task_per_thread[thr].shared_tasklet_list)),
!(LIST_ISEMPTY(&task_per_thread[thr].tasklets[TL_URGENT]) &&
LIST_ISEMPTY(&task_per_thread[thr].tasklets[TL_NORMAL]) &&
LIST_ISEMPTY(&task_per_thread[thr].tasklets[TL_BULK]) &&
MT_LIST_ISEMPTY(&task_per_thread[thr].shared_tasklet_list)),
task_per_thread[thr].task_list_size,
task_per_thread[thr].rqueue_size,
stuck,

27
src/task.c
View File

@ -427,7 +427,7 @@ void process_runnable_tasks()
*/
tmp_list = MT_LIST_BEHEAD(&sched->shared_tasklet_list);
if (tmp_list)
LIST_SPLICE_END_DETACHED(&sched->task_list, (struct list *)tmp_list);
LIST_SPLICE_END_DETACHED(&sched->tasklets[TL_URGENT], (struct list *)tmp_list);
tasks_run_queue_cur = tasks_run_queue; /* keep a copy for reporting */
nb_tasks_cur = nb_tasks;
@ -436,9 +436,15 @@ void process_runnable_tasks()
if (likely(niced_tasks))
max_processed = (max_processed + 3) / 4;
/* run up to 3*max_processed/4 urgent tasklets */
done = run_tasks_from_list(&tt->tasklets[TL_URGENT], 3*(max_processed + 1) / 4);
max_processed -= done;
/* pick up to (max_processed-done+1)/2 regular tasks from prio-ordered run queues */
/* Note: the grq lock is always held when grq is not null */
while (tt->task_list_size < max_processed) {
while (tt->task_list_size < (max_processed + 1) / 2) {
if ((global_tasks_mask & tid_bit) && !grq) {
#ifdef USE_THREAD
HA_SPIN_LOCK(TASK_RQ_LOCK, &rq_lock);
@ -489,7 +495,7 @@ void process_runnable_tasks()
/* Make sure the entry doesn't appear to be in a list */
LIST_INIT(&((struct tasklet *)t)->list);
/* And add it to the local task list */
tasklet_insert_into_tasklet_list((struct tasklet *)t);
tasklet_insert_into_tasklet_list(&tt->tasklets[TL_NORMAL], (struct tasklet *)t);
tt->task_list_size++;
activity[tid].tasksw++;
}
@ -500,10 +506,17 @@ void process_runnable_tasks()
grq = NULL;
}
done = run_tasks_from_list(&tt->task_list, max_processed);
/* run between max_processed/8 and max_processed/2 regular tasks */
done = run_tasks_from_list(&tt->tasklets[TL_NORMAL], (max_processed + 1) / 2);
max_processed -= done;
if (!LIST_ISEMPTY(&tt->task_list))
/* run between max_processed/8 and max_processed bulk tasklets */
done = run_tasks_from_list(&tt->tasklets[TL_BULK], max_processed);
max_processed -= done;
if (!LIST_ISEMPTY(&sched->tasklets[TL_URGENT]) |
!LIST_ISEMPTY(&sched->tasklets[TL_NORMAL]) |
!LIST_ISEMPTY(&sched->tasklets[TL_BULK]))
activity[tid].long_rq++;
}
@ -607,7 +620,9 @@ static void init_task()
#endif
memset(&task_per_thread, 0, sizeof(task_per_thread));
for (i = 0; i < MAX_THREADS; i++) {
LIST_INIT(&task_per_thread[i].task_list);
LIST_INIT(&task_per_thread[i].tasklets[TL_URGENT]);
LIST_INIT(&task_per_thread[i].tasklets[TL_NORMAL]);
LIST_INIT(&task_per_thread[i].tasklets[TL_BULK]);
MT_LIST_INIT(&task_per_thread[i].shared_tasklet_list);
}
}