Commit 8ee36e04 authored by Chris Wilson's avatar Chris Wilson
Browse files

drm/i915/execlists: Minimalistic timeslicing



If we have multiple contexts of equal priority pending execution,
activate a timer to demote the currently executing context in favour of
the next in the queue when that timeslice expires. This enforces
fairness between contexts (so long as they allow preemption -- forced
preemption, in the future, will kick those who do not obey) and allows
us to avoid userspace blocking forward progress with e.g. unbounded
MI_SEMAPHORE_WAIT.

For the starting point here, we use the jiffie as our timeslice so that
we should be reasonably efficient wrt frequent CPU wakeups.

Testcase: igt/gem_exec_scheduler/semaphore-resolve
Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: default avatarMika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190620142052.19311-2-chris@chris-wilson.co.uk
parent 22b7a426
......@@ -12,6 +12,7 @@
#include <linux/kref.h>
#include <linux/list.h>
#include <linux/llist.h>
#include <linux/timer.h>
#include <linux/types.h>
#include "i915_gem.h"
......@@ -149,6 +150,11 @@ struct intel_engine_execlists {
*/
struct tasklet_struct tasklet;
/**
* @timer: kick the current context if its timeslice expires
*/
struct timer_list timer;
/**
* @default_priolist: priority list for I915_PRIORITY_NORMAL
*/
......
......@@ -266,6 +266,7 @@ static int effective_prio(const struct i915_request *rq)
prio |= I915_PRIORITY_NOSEMAPHORE;
/* Restrict mere WAIT boosts from triggering preemption */
BUILD_BUG_ON(__NO_PREEMPTION & ~I915_PRIORITY_MASK); /* only internal */
return prio | __NO_PREEMPTION;
}
......@@ -830,6 +831,81 @@ last_active(const struct intel_engine_execlists *execlists)
return *last;
}
static void
defer_request(struct i915_request * const rq, struct list_head * const pl)
{
struct i915_dependency *p;
/*
* We want to move the interrupted request to the back of
* the round-robin list (i.e. its priority level), but
* in doing so, we must then move all requests that were in
* flight and were waiting for the interrupted request to
* be run after it again.
*/
list_move_tail(&rq->sched.link, pl);
list_for_each_entry(p, &rq->sched.waiters_list, wait_link) {
struct i915_request *w =
container_of(p->waiter, typeof(*w), sched);
/* Leave semaphores spinning on the other engines */
if (w->engine != rq->engine)
continue;
/* No waiter should start before the active request completed */
GEM_BUG_ON(i915_request_started(w));
GEM_BUG_ON(rq_prio(w) > rq_prio(rq));
if (rq_prio(w) < rq_prio(rq))
continue;
if (list_empty(&w->sched.link))
continue; /* Not yet submitted; unready */
/*
* This should be very shallow as it is limited by the
* number of requests that can fit in a ring (<64) and
* the number of contexts that can be in flight on this
* engine.
*/
defer_request(w, pl);
}
}
static void defer_active(struct intel_engine_cs *engine)
{
struct i915_request *rq;
rq = __unwind_incomplete_requests(engine);
if (!rq)
return;
defer_request(rq, i915_sched_lookup_priolist(engine, rq_prio(rq)));
}
static bool
need_timeslice(struct intel_engine_cs *engine, const struct i915_request *rq)
{
int hint;
if (list_is_last(&rq->sched.link, &engine->active.requests))
return false;
hint = max(rq_prio(list_next_entry(rq, sched.link)),
engine->execlists.queue_priority_hint);
return hint >= rq_prio(rq);
}
static bool
enable_timeslice(struct intel_engine_cs *engine)
{
struct i915_request *last = last_active(&engine->execlists);
return last && need_timeslice(engine, last);
}
static void execlists_dequeue(struct intel_engine_cs *engine)
{
struct intel_engine_execlists * const execlists = &engine->execlists;
......@@ -923,6 +999,32 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
*/
last->hw_context->lrc_desc |= CTX_DESC_FORCE_RESTORE;
last = NULL;
} else if (need_timeslice(engine, last) &&
!timer_pending(&engine->execlists.timer)) {
GEM_TRACE("%s: expired last=%llx:%lld, prio=%d, hint=%d\n",
engine->name,
last->fence.context,
last->fence.seqno,
last->sched.attr.priority,
execlists->queue_priority_hint);
ring_set_paused(engine, 1);
defer_active(engine);
/*
* Unlike for preemption, if we rewind and continue
* executing the same context as previously active,
* the order of execution will remain the same and
* the tail will only advance. We do not need to
* force a full context restore, as a lite-restore
* is sufficient to resample the monotonic TAIL.
*
* If we switch to any other context, similarly we
* will not rewind TAIL of current context, and
* normal save/restore will preserve state and allow
* us to later continue executing the same request.
*/
last = NULL;
} else {
/*
* Otherwise if we already have a request pending
......@@ -1247,6 +1349,9 @@ static void process_csb(struct intel_engine_cs *engine)
sizeof(*execlists->pending));
execlists->pending[0] = NULL;
if (enable_timeslice(engine))
mod_timer(&execlists->timer, jiffies + 1);
if (!inject_preempt_hang(execlists))
ring_set_paused(engine, 0);
} else if (status & GEN8_CTX_STATUS_PREEMPTED) {
......@@ -1317,6 +1422,15 @@ static void execlists_submission_tasklet(unsigned long data)
spin_unlock_irqrestore(&engine->active.lock, flags);
}
static void execlists_submission_timer(struct timer_list *timer)
{
struct intel_engine_cs *engine =
from_timer(engine, timer, execlists.timer);
/* Kick the tasklet for some interrupt coalescing and reset handling */
tasklet_hi_schedule(&engine->execlists.tasklet);
}
static void queue_request(struct intel_engine_cs *engine,
struct i915_sched_node *node,
int prio)
......@@ -2542,6 +2656,7 @@ static int gen8_init_rcs_context(struct i915_request *rq)
static void execlists_park(struct intel_engine_cs *engine)
{
del_timer_sync(&engine->execlists.timer);
intel_engine_park(engine);
}
......@@ -2639,6 +2754,7 @@ int intel_execlists_submission_setup(struct intel_engine_cs *engine)
tasklet_init(&engine->execlists.tasklet,
execlists_submission_tasklet, (unsigned long)engine);
timer_setup(&engine->execlists.timer, execlists_submission_timer, 0);
logical_ring_default_vfuncs(engine);
logical_ring_default_irqs(engine);
......
......@@ -79,6 +79,225 @@ static int live_sanitycheck(void *arg)
return err;
}
static int
emit_semaphore_chain(struct i915_request *rq, struct i915_vma *vma, int idx)
{
u32 *cs;
cs = intel_ring_begin(rq, 10);
if (IS_ERR(cs))
return PTR_ERR(cs);
*cs++ = MI_ARB_ON_OFF | MI_ARB_ENABLE;
*cs++ = MI_SEMAPHORE_WAIT |
MI_SEMAPHORE_GLOBAL_GTT |
MI_SEMAPHORE_POLL |
MI_SEMAPHORE_SAD_NEQ_SDD;
*cs++ = 0;
*cs++ = i915_ggtt_offset(vma) + 4 * idx;
*cs++ = 0;
if (idx > 0) {
*cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
*cs++ = i915_ggtt_offset(vma) + 4 * (idx - 1);
*cs++ = 0;
*cs++ = 1;
} else {
*cs++ = MI_NOOP;
*cs++ = MI_NOOP;
*cs++ = MI_NOOP;
*cs++ = MI_NOOP;
}
*cs++ = MI_ARB_ON_OFF | MI_ARB_DISABLE;
intel_ring_advance(rq, cs);
return 0;
}
static struct i915_request *
semaphore_queue(struct intel_engine_cs *engine, struct i915_vma *vma, int idx)
{
struct i915_gem_context *ctx;
struct i915_request *rq;
int err;
ctx = kernel_context(engine->i915);
if (!ctx)
return ERR_PTR(-ENOMEM);
rq = igt_request_alloc(ctx, engine);
if (IS_ERR(rq))
goto out_ctx;
err = emit_semaphore_chain(rq, vma, idx);
i915_request_add(rq);
if (err)
rq = ERR_PTR(err);
out_ctx:
kernel_context_close(ctx);
return rq;
}
static int
release_queue(struct intel_engine_cs *engine,
struct i915_vma *vma,
int idx)
{
struct i915_sched_attr attr = {
.priority = I915_USER_PRIORITY(I915_PRIORITY_MAX),
};
struct i915_request *rq;
u32 *cs;
rq = i915_request_create(engine->kernel_context);
if (IS_ERR(rq))
return PTR_ERR(rq);
cs = intel_ring_begin(rq, 4);
if (IS_ERR(cs)) {
i915_request_add(rq);
return PTR_ERR(cs);
}
*cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
*cs++ = i915_ggtt_offset(vma) + 4 * (idx - 1);
*cs++ = 0;
*cs++ = 1;
intel_ring_advance(rq, cs);
i915_request_add(rq);
engine->schedule(rq, &attr);
return 0;
}
static int
slice_semaphore_queue(struct intel_engine_cs *outer,
struct i915_vma *vma,
int count)
{
struct intel_engine_cs *engine;
struct i915_request *head;
enum intel_engine_id id;
int err, i, n = 0;
head = semaphore_queue(outer, vma, n++);
if (IS_ERR(head))
return PTR_ERR(head);
i915_request_get(head);
for_each_engine(engine, outer->i915, id) {
for (i = 0; i < count; i++) {
struct i915_request *rq;
rq = semaphore_queue(engine, vma, n++);
if (IS_ERR(rq)) {
err = PTR_ERR(rq);
goto out;
}
}
}
err = release_queue(outer, vma, n);
if (err)
goto out;
if (i915_request_wait(head,
I915_WAIT_LOCKED,
2 * RUNTIME_INFO(outer->i915)->num_engines * (count + 2) * (count + 3)) < 0) {
pr_err("Failed to slice along semaphore chain of length (%d, %d)!\n",
count, n);
GEM_TRACE_DUMP();
i915_gem_set_wedged(outer->i915);
err = -EIO;
}
out:
i915_request_put(head);
return err;
}
static int live_timeslice_preempt(void *arg)
{
struct drm_i915_private *i915 = arg;
struct drm_i915_gem_object *obj;
intel_wakeref_t wakeref;
struct i915_vma *vma;
void *vaddr;
int err = 0;
int count;
/*
* If a request takes too long, we would like to give other users
* a fair go on the GPU. In particular, users may create batches
* that wait upon external input, where that input may even be
* supplied by another GPU job. To avoid blocking forever, we
* need to preempt the current task and replace it with another
* ready task.
*/
mutex_lock(&i915->drm.struct_mutex);
wakeref = intel_runtime_pm_get(&i915->runtime_pm);
obj = i915_gem_object_create_internal(i915, PAGE_SIZE);
if (IS_ERR(obj)) {
err = PTR_ERR(obj);
goto err_unlock;
}
vma = i915_vma_instance(obj, &i915->ggtt.vm, NULL);
if (IS_ERR(vma)) {
err = PTR_ERR(vma);
goto err_obj;
}
vaddr = i915_gem_object_pin_map(obj, I915_MAP_WC);
if (IS_ERR(vaddr)) {
err = PTR_ERR(vaddr);
goto err_obj;
}
err = i915_vma_pin(vma, 0, 0, PIN_GLOBAL);
if (err)
goto err_map;
for_each_prime_number_from(count, 1, 16) {
struct intel_engine_cs *engine;
enum intel_engine_id id;
for_each_engine(engine, i915, id) {
memset(vaddr, 0, PAGE_SIZE);
err = slice_semaphore_queue(engine, vma, count);
if (err)
goto err_pin;
if (igt_flush_test(i915, I915_WAIT_LOCKED)) {
err = -EIO;
goto err_pin;
}
}
}
err_pin:
i915_vma_unpin(vma);
err_map:
i915_gem_object_unpin_map(obj);
err_obj:
i915_gem_object_put(obj);
err_unlock:
if (igt_flush_test(i915, I915_WAIT_LOCKED))
err = -EIO;
intel_runtime_pm_put(&i915->runtime_pm, wakeref);
mutex_unlock(&i915->drm.struct_mutex);
return err;
}
static int live_busywait_preempt(void *arg)
{
struct drm_i915_private *i915 = arg;
......@@ -398,6 +617,9 @@ static int live_late_preempt(void *arg)
if (!ctx_lo)
goto err_ctx_hi;
/* Make sure ctx_lo stays before ctx_hi until we trigger preemption. */
ctx_lo->sched.priority = I915_USER_PRIORITY(1);
for_each_engine(engine, i915, id) {
struct igt_live_test t;
struct i915_request *rq;
......@@ -1812,6 +2034,7 @@ int intel_execlists_live_selftests(struct drm_i915_private *i915)
{
static const struct i915_subtest tests[] = {
SUBTEST(live_sanitycheck),
SUBTEST(live_timeslice_preempt),
SUBTEST(live_busywait_preempt),
SUBTEST(live_preempt),
SUBTEST(live_late_preempt),
......
......@@ -394,6 +394,7 @@ bool __i915_sched_node_add_dependency(struct i915_sched_node *node,
list_add(&dep->wait_link, &signal->waiters_list);
list_add(&dep->signal_link, &node->signalers_list);
dep->signaler = signal;
dep->waiter = node;
dep->flags = flags;
/* Keep track of whether anyone on this chain has a semaphore */
......
......@@ -62,6 +62,7 @@ struct i915_sched_node {
struct i915_dependency {
struct i915_sched_node *signaler;
struct i915_sched_node *waiter;
struct list_head signal_link;
struct list_head wait_link;
struct list_head dfs_link;
......
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