Re: [PATCH i-g-t 13/16] i915: Add gem_exec_balancer

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Tvrtko Ursulin (2019-05-15 11:49:45)
> 
> On 08/05/2019 11:09, Chris Wilson wrote:
> > Exercise the in-kernel load balancer checking that we can distribute
> > batches across the set of ctx->engines to avoid load.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > ---
> >   tests/Makefile.am              |    1 +
> >   tests/Makefile.sources         |    1 +
> >   tests/i915/gem_exec_balancer.c | 1050 ++++++++++++++++++++++++++++++++
> >   tests/meson.build              |    7 +
> >   4 files changed, 1059 insertions(+)
> >   create mode 100644 tests/i915/gem_exec_balancer.c
> > 
> > diff --git a/tests/Makefile.am b/tests/Makefile.am
> > index 5097debf6..c6af0aeaf 100644
> > --- a/tests/Makefile.am
> > +++ b/tests/Makefile.am
> > @@ -96,6 +96,7 @@ gem_close_race_LDADD = $(LDADD) -lpthread
> >   gem_ctx_thrash_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> >   gem_ctx_thrash_LDADD = $(LDADD) -lpthread
> >   gem_ctx_sseu_LDADD = $(LDADD) $(top_builddir)/lib/libigt_perf.la
> > +i915_gem_exec_balancer_LDADD = $(LDADD) $(top_builddir)/lib/libigt_perf.la
> >   gem_exec_capture_LDADD = $(LDADD) -lz
> >   gem_exec_parallel_CFLAGS = $(AM_CFLAGS) $(THREAD_CFLAGS)
> >   gem_exec_parallel_LDADD = $(LDADD) -lpthread
> > diff --git a/tests/Makefile.sources b/tests/Makefile.sources
> > index e7ee27e81..323b625aa 100644
> > --- a/tests/Makefile.sources
> > +++ b/tests/Makefile.sources
> > @@ -24,6 +24,7 @@ TESTS_progs = \
> >       i915/gem_ctx_clone \
> >       i915/gem_ctx_engines \
> >       i915/gem_ctx_shared \
> > +     i915/gem_exec_balancer \
> >       i915/gem_vm_create \
> >       kms_3d \
> >       kms_addfb_basic \
> > diff --git a/tests/i915/gem_exec_balancer.c b/tests/i915/gem_exec_balancer.c
> > new file mode 100644
> > index 000000000..25195d478
> > --- /dev/null
> > +++ b/tests/i915/gem_exec_balancer.c
> > @@ -0,0 +1,1050 @@
> > +/*
> > + * Copyright © 2018 Intel Corporation
> 
> 2019 I guess, even though work was started in 2018?
> 
> > + *
> > + * Permission is hereby granted, free of charge, to any person obtaining a
> > + * copy of this software and associated documentation files (the "Software"),
> > + * to deal in the Software without restriction, including without limitation
> > + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> > + * and/or sell copies of the Software, and to permit persons to whom the
> > + * Software is furnished to do so, subject to the following conditions:
> > + *
> > + * The above copyright notice and this permission notice (including the next
> > + * paragraph) shall be included in all copies or substantial portions of the
> > + * Software.
> > + *
> > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> > + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> > + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> > + * IN THE SOFTWARE.
> > + */
> > +
> > +#include <sched.h>
> > +
> > +#include "igt.h"
> > +#include "igt_perf.h"
> > +#include "i915/gem_ring.h"
> > +#include "sw_sync.h"
> > +
> > +IGT_TEST_DESCRIPTION("Exercise in-kernel load-balancing");
> > +
> > +#define INSTANCE_COUNT (1 << I915_PMU_SAMPLE_INSTANCE_BITS)
> 
> Hmm.. this is a strange surrogate but I guess it works.
> 
> > +
> > +static bool has_class_instance(int i915, uint16_t class, uint16_t instance)
> > +{
> > +     int fd;
> > +
> > +     fd = perf_i915_open(I915_PMU_ENGINE_BUSY(class, instance));
> 
> More work for Andi to replace with real engine discovery. :)
> 
> > +     if (fd != -1) {
> > +             close(fd);
> > +             return true;
> > +     }
> > +
> > +     return false;
> > +}
> > +
> > +static struct i915_engine_class_instance *
> > +list_engines(int i915, uint32_t class_mask, unsigned int *out)
> > +{
> > +     unsigned int count = 0, size = 64;
> > +     struct i915_engine_class_instance *engines;
> > +
> > +     engines = malloc(size * sizeof(*engines));
> > +     if (!engines) {
> > +             *out = 0;
> > +             return NULL;
> > +     }
> > +
> > +     for (enum drm_i915_gem_engine_class class = I915_ENGINE_CLASS_RENDER;
> > +          class_mask;
> > +          class++, class_mask >>= 1) {
> > +             if (!(class_mask & 1))
> > +                     continue;
> > +
> > +             for (unsigned int instance = 0;
> > +                  instance < INSTANCE_COUNT;
> > +                  instance++) {
> > +                  if (!has_class_instance(i915, class, instance))
> > +                          continue;
> > +
> > +                     if (count == size) {
> > +                             struct i915_engine_class_instance *e;
> > +
> > +                             size *= 2;
> > +                             e = realloc(engines, size*sizeof(*engines));
> > +                             if (!e) {
> 
> I'd just assert. On malloc as well.
> 
> > +                                     *out = count;
> > +                                     return engines;
> > +                             }
> > +
> > +                             engines = e;
> > +                     }
> > +
> > +                     engines[count++] = (struct i915_engine_class_instance){
> > +                             .engine_class = class,
> > +                             .engine_instance = instance,
> > +                     };
> > +             }
> > +     }
> > +
> > +     if (!count) {
> > +             free(engines);
> > +             engines = NULL;
> > +     }
> > +
> > +     *out = count;
> > +     return engines;
> > +}
> > +
> > +static int __set_load_balancer(int i915, uint32_t ctx,
> > +                            const struct i915_engine_class_instance *ci,
> > +                            unsigned int count)
> > +{
> > +     I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(balancer, count);
> > +     I915_DEFINE_CONTEXT_PARAM_ENGINES(engines, 1 + count);
> > +     struct drm_i915_gem_context_param p = {
> > +             .ctx_id = ctx,
> > +             .param = I915_CONTEXT_PARAM_ENGINES,
> > +             .size = sizeof(engines),
> > +             .value = to_user_pointer(&engines)
> > +     };
> > +
> > +     memset(&balancer, 0, sizeof(balancer));
> > +     balancer.base.name = I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE;
> > +
> > +     igt_assert(count);
> > +     balancer.num_siblings = count;
> > +     memcpy(balancer.engines, ci, count * sizeof(*ci));
> > +
> > +     memset(&engines, 0, sizeof(engines));
> > +     engines.extensions = to_user_pointer(&balancer);
> > +     engines.engines[0].engine_class =
> > +             I915_ENGINE_CLASS_INVALID;
> > +     engines.engines[0].engine_instance =
> > +             I915_ENGINE_CLASS_INVALID_NONE;
> > +     memcpy(engines.engines + 1, ci, count * sizeof(*ci));
> > +
> > +     return __gem_context_set_param(i915, &p);
> > +}
> > +
> > +static void set_load_balancer(int i915, uint32_t ctx,
> > +                           const struct i915_engine_class_instance *ci,
> > +                           unsigned int count)
> > +{
> > +     igt_assert_eq(__set_load_balancer(i915, ctx, ci, count), 0);
> > +}
> > +
> > +static uint32_t load_balancer_create(int i915,
> > +                                  const struct i915_engine_class_instance *ci,
> > +                                  unsigned int count)
> > +{
> > +     uint32_t ctx;
> > +
> > +     ctx = gem_context_create(i915);
> > +     set_load_balancer(i915, ctx, ci, count);
> > +
> > +     return ctx;
> > +}
> > +
> > +static uint32_t __batch_create(int i915, uint32_t offset)
> > +{
> > +     const uint32_t bbe = MI_BATCH_BUFFER_END;
> > +     uint32_t handle;
> > +
> > +     handle = gem_create(i915, ALIGN(offset + 4, 4096));
> > +     gem_write(i915, handle, offset, &bbe, sizeof(bbe));
> > +
> > +     return handle;
> > +}
> > +
> > +static uint32_t batch_create(int i915)
> > +{
> > +     return __batch_create(i915, 0);
> > +}
> > +
> > +static void invalid_balancer(int i915)
> > +{
> > +     I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(balancer, 64);
> > +     I915_DEFINE_CONTEXT_PARAM_ENGINES(engines, 64);
> > +     struct drm_i915_gem_context_param p = {
> > +             .param = I915_CONTEXT_PARAM_ENGINES,
> > +             .value = to_user_pointer(&engines)
> > +     };
> > +     uint32_t handle;
> > +     void *ptr;
> > +
> > +     /*
> > +      * Assume that I915_CONTEXT_PARAM_ENGINE validates the array
> > +      * of engines[], our job is to determine if the load_balancer
> > +      * extension explodes.
> > +      */
> > +
> > +     for (int class = 0; class < 32; class++) {
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +
> > +             ci = list_engines(i915, 1 << class, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             igt_debug("Found %d engines\n", count);
> > +             igt_assert_lte(count, 64);
> 
> Hey.. you always say trust the kernel! ;)

This code was placeholder that you said you would replace by a proper
query api...

> 
> > +
> > +             p.ctx_id = gem_context_create(i915);
> > +             p.size = (sizeof(struct i915_context_param_engines) +
> > +                             (count + 1) * sizeof(*engines.engines));
> 
> Alignment looks off.
> 
> > +
> > +             memset(&engines, 0, sizeof(engines));
> > +             engines.engines[0].engine_class = I915_ENGINE_CLASS_INVALID;
> > +             engines.engines[0].engine_instance = I915_ENGINE_CLASS_INVALID_NONE;
> > +             memcpy(engines.engines + 1, ci, count * sizeof(*ci));
> > +             gem_context_set_param(i915, &p);
> > +
> > +             engines.extensions = -1ull;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +
> > +             engines.extensions = 1ull;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +
> > +             memset(&balancer, 0, sizeof(balancer));
> > +             balancer.base.name = I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE;
> > +             balancer.num_siblings = count;
> > +             memcpy(balancer.engines, ci, count * sizeof(*ci));
> > +
> > +             engines.extensions = to_user_pointer(&balancer);
> > +             gem_context_set_param(i915, &p);
> > +
> > +             balancer.engine_index = 1;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EEXIST);
> > +
> > +             balancer.engine_index = count;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EEXIST);
> > +
> > +             balancer.engine_index = count + 1;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EINVAL);
> > +
> > +             balancer.engine_index = 0;
> > +             gem_context_set_param(i915, &p);
> > +
> > +             balancer.base.next_extension = to_user_pointer(&balancer);
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EEXIST);
> > +
> > +             balancer.base.next_extension = -1ull;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +
> > +             handle = gem_create(i915, 4096 * 3);
> > +             ptr = gem_mmap__gtt(i915, handle, 4096 * 3, PROT_WRITE);
> > +             gem_close(i915, handle);
> > +
> > +             memset(&engines, 0, sizeof(engines));
> > +             engines.engines[0].engine_class = I915_ENGINE_CLASS_INVALID;
> > +             engines.engines[0].engine_instance = I915_ENGINE_CLASS_INVALID_NONE;
> > +             engines.engines[1].engine_class = I915_ENGINE_CLASS_INVALID;
> > +             engines.engines[1].engine_instance = I915_ENGINE_CLASS_INVALID_NONE;
> > +             memcpy(engines.engines + 2, ci, count * sizeof(ci));
> > +             p.size = (sizeof(struct i915_context_param_engines) +
> > +                             (count + 2) * sizeof(*engines.engines));
> 
> Alignment again.
> 
> > +             gem_context_set_param(i915, &p);
> > +
> > +             balancer.base.next_extension = 0;
> > +             balancer.engine_index = 1;
> > +             engines.extensions = to_user_pointer(&balancer);
> > +             gem_context_set_param(i915, &p);
> > +
> > +             memcpy(ptr + 4096 - 8, &balancer, sizeof(balancer));
> > +             memcpy(ptr + 8192 - 8, &balancer, sizeof(balancer));
> > +             balancer.engine_index = 0;
> > +
> > +             engines.extensions = to_user_pointer(ptr) + 4096 - 8;
> > +             gem_context_set_param(i915, &p);
> > +
> > +             balancer.base.next_extension = engines.extensions;
> > +             engines.extensions = to_user_pointer(&balancer);
> > +             gem_context_set_param(i915, &p);
> 
> mmap_gtt and unmapped area testing in one?

Neighbouring.

> > +             munmap(ptr, 4096); >+           igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +             engines.extensions = to_user_pointer(ptr) + 4096 - 8;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +
> > +             engines.extensions = to_user_pointer(ptr) + 8192 - 8;
> > +             gem_context_set_param(i915, &p);
> > +
> > +             balancer.base.next_extension = engines.extensions;
> > +             engines.extensions = to_user_pointer(&balancer);
> > +             gem_context_set_param(i915, &p);
> > +
> > +             munmap(ptr + 8192, 4096);
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +             engines.extensions = to_user_pointer(ptr) + 8192 - 8;
> > +             igt_assert_eq(__gem_context_set_param(i915, &p), -EFAULT);
> > +
> > +             munmap(ptr + 4096, 4096);
> > +
> > +             gem_context_destroy(i915, p.ctx_id);
> > +             free(ci);
> > +     }
> > +}
> > +
> > +static void kick_kthreads(int period_us)
> > +{
> > +     sched_yield();
> > +     usleep(period_us);
> 
> yield and sleep hm.. calling with zero period_us? Doesn't seem like it. 
> So what's it about?

Historically yield may have been a no-op, but sleep(0) actually yielded.

> > +}
> > +
> > +static double measure_load(int pmu, int period_us)
> > +{
> > +     uint64_t data[2];
> > +     uint64_t d_t, d_v;
> > +
> > +     kick_kthreads(period_us);
> > +
> > +     igt_assert_eq(read(pmu, data, sizeof(data)), sizeof(data));
> > +     d_v = -data[0];
> > +     d_t = -data[1];
> > +
> > +     usleep(period_us);
> > +
> > +     igt_assert_eq(read(pmu, data, sizeof(data)), sizeof(data));
> > +     d_v += data[0];
> > +     d_t += data[1];
> 
> This -val + val trick with uint64_t works?

Yes, unsigned overflow is defined.

> 
> > +
> > +     return d_v / (double)d_t;
> > +}
> > +
> > +static double measure_min_load(int pmu, unsigned int num, int period_us)
> > +{
> > +     uint64_t data[2 + num];
> > +     uint64_t d_t, d_v[num];
> > +     uint64_t min = -1, max = 0;
> > +
> > +     kick_kthreads(period_us);
> > +
> > +     igt_assert_eq(read(pmu, data, sizeof(data)), sizeof(data));
> > +     for (unsigned int n = 0; n < num; n++)
> > +             d_v[n] = -data[2 + n];
> > +     d_t = -data[1];
> > +
> > +     usleep(period_us);
> > +
> > +     igt_assert_eq(read(pmu, data, sizeof(data)), sizeof(data));
> > +
> > +     d_t += data[1];
> > +     for (unsigned int n = 0; n < num; n++) {
> > +             d_v[n] += data[2 + n];
> > +             igt_debug("engine[%d]: %.1f%%\n",
> > +                       n, d_v[n] / (double)d_t * 100);
> > +             if (d_v[n] < min)
> > +                     min = d_v[n];
> > +             if (d_v[n] > max)
> > +                     max = d_v[n];
> > +     }
> > +
> > +     igt_debug("elapsed: %"PRIu64"ns, load [%.1f, %.1f]%%\n",
> > +               d_t, min / (double)d_t * 100,  max / (double)d_t * 100);
> > +
> > +     return min / (double)d_t;
> > +}
> > +
> > +static void check_individual_engine(int i915,
> > +                                 uint32_t ctx,
> > +                                 const struct i915_engine_class_instance *ci,
> > +                                 int idx)
> > +{
> > +     igt_spin_t *spin;
> > +     double load;
> > +     int pmu;
> > +
> > +     pmu = perf_i915_open(I915_PMU_ENGINE_BUSY(ci[idx].engine_class,
> > +                                               ci[idx].engine_instance));
> > +
> > +     spin = igt_spin_new(i915, .ctx = ctx, .engine = idx + 1);
> > +     load = measure_load(pmu, 10000);
> 
> Hm usleep before start of measuring and between two samples is the same. 
> The one before should be fixed I think, no?

Could be, that would require thought as to what the appropriate period
for kicking should be. Yay for ksoftirqd.

> > +     igt_spin_free(i915, spin);
> > +
> > +     close(pmu);
> > +
> > +     igt_assert_f(load > 0.90,
> > +                  "engine %d (class:instance %d:%d) was found to be only %.1f%% busy\n",
> > +                  idx, ci[idx].engine_class, ci[idx].engine_instance, load*100);
> > +}
> > +
> > +static void individual(int i915)
> > +{
> > +     uint32_t ctx;
> > +
> > +     /*
> > +      * I915_CONTEXT_PARAM_ENGINE allows us to index into the user
> > +      * supplied array from gem_execbuf(). Our check is to build the
> > +      * ctx->engine[] with various different engine classes, feed in
> > +      * a spinner and then ask pmu to confirm it the expected engine
> > +      * was busy.
> > +      */
> > +
> > +     ctx = gem_context_create(i915);
> > +
> > +     for (int mask = 0; mask < 32; mask++) {
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +
> > +             ci = list_engines(i915, 1u << mask, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, mask);
> > +
> > +             for (int pass = 0; pass < count; pass++) { /* approx. count! */
> > +                     igt_permute_array(ci, count, igt_exchange_int64);
> 
> struct i915_engine_class_instance is four bytes long, so swap func looks 
> wrong. Unless for some reason you want to swap in blocks of two. Don't 
> know. Last index would grab into random memory though. I must be missing 
> something or it wouldn't have worked..

Once upon a time class_instance was 2xu32.

> 
> > +                     set_load_balancer(i915, ctx, ci, count);
> > +                     for (unsigned int n = 0; n < count; n++)
> > +                             check_individual_engine(i915, ctx, ci, n);
> > +             }
> > +
> > +             free(ci);
> > +     }
> > +
> > +     gem_context_destroy(i915, ctx);
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static void indicies(int i915)
> 
> indices?
> 
> > +{
> > +     I915_DEFINE_CONTEXT_PARAM_ENGINES(engines, I915_EXEC_RING_MASK + 1);
> > +     struct drm_i915_gem_context_param p = {
> > +             .ctx_id = gem_context_create(i915),
> > +             .param = I915_CONTEXT_PARAM_ENGINES,
> > +             .value = to_user_pointer(&engines)
> > +     };
> > +
> > +     struct drm_i915_gem_exec_object2 batch = {
> > +             .handle = batch_create(i915),
> > +     };
> > +
> > +     unsigned int nengines = 0;
> > +     void *balancers = NULL;
> > +
> > +     /*
> > +      * We can populate our engine map with multiple virtual engines.
> > +      * Do so.
> > +      */
> > +
> > +     for (int class = 0; class < 32; class++) {
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +
> > +             ci = list_engines(i915, 1u << class, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, class);
> 
> Maybe this debug message should go into list_engines, since it seems 
> repeated a few times already.

Or remove the debug, I hear you.

> > +
> > +             for (int n = 0; n < count; n++) {
> > +                     I915_DEFINE_CONTEXT_ENGINES_LOAD_BALANCE(*balancer,
> > +                                                              count);
> > +
> > +                     engines.engines[nengines].engine_class =
> > +                             I915_ENGINE_CLASS_INVALID;
> > +                     engines.engines[nengines].engine_instance =
> > +                             I915_ENGINE_CLASS_INVALID_NONE;
> > +
> > +                     balancer = calloc(sizeof(*balancer), 1);
> > +                     igt_assert(balancer);
> > +
> > +                     balancer->base.name =
> > +                             I915_CONTEXT_ENGINES_EXT_LOAD_BALANCE;
> > +                     balancer->base.next_extension =
> > +                             to_user_pointer(balancers);
> > +                     balancers = balancer;
> > +
> > +                     balancer->engine_index = nengines++;
> > +                     balancer->num_siblings = count;
> > +
> > +                     memcpy(balancer->engines,
> > +                            ci, count * sizeof(*ci));
> > +             }
> > +             free(ci);
> > +     }
> > +
> > +     igt_require(balancers);
> > +     engines.extensions = to_user_pointer(balancers);
> > +     p.size = (sizeof(struct i915_engine_class_instance) * nengines +
> > +               sizeof(struct i915_context_param_engines));
> > +     gem_context_set_param(i915, &p);
> > +
> > +     for (unsigned int n = 0; n < nengines; n++) {
> > +             struct drm_i915_gem_execbuffer2 eb = {
> > +                     .buffers_ptr = to_user_pointer(&batch),
> > +                     .buffer_count = 1,
> > +                     .flags = n,
> > +                     .rsvd1 = p.ctx_id,
> > +             };
> > +             igt_debug("Executing on index=%d\n", n);
> > +             gem_execbuf(i915, &eb);
> > +     }
> > +     gem_context_destroy(i915, p.ctx_id);
> > +
> > +     gem_sync(i915, batch.handle);
> > +     gem_close(i915, batch.handle);
> > +
> > +     while (balancers) {
> > +             struct i915_context_engines_load_balance *b, *n;
> > +
> > +             b = balancers;
> > +             n = from_user_pointer(b->base.next_extension);
> > +             free(b);
> > +
> > +             balancers = n;
> > +     }
> > +
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static void busy(int i915)
> > +{
> > +     uint32_t scratch = gem_create(i915, 4096);
> > +
> > +     /*
> > +      * Check that virtual engines are reported via GEM_BUSY.
> > +      *
> > +      * When running, the batch will be on the real engine and report
> > +      * the actual class.
> > +      *
> > +      * Prior to running, if the load-balancer is across multiple
> > +      * classes we don't know which engine the batch will
> > +      * execute on, so we report them all!
> > +      *
> > +      * However, as we only support (and test) creating a load-balancer
> > +      * from engines of only one class, that can be propagated accurately
> > +      * through to GEM_BUSY.
> > +      */
> > +
> > +     for (int class = 0; class < 16; class++) {
> > +             struct drm_i915_gem_busy busy;
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +             igt_spin_t *spin[2];
> > +             uint32_t ctx;
> > +
> > +             ci = list_engines(i915, 1u << class, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, class);
> > +             ctx = load_balancer_create(i915, ci, count);
> > +             free(ci);
> > +
> > +             spin[0] = __igt_spin_new(i915,
> > +                                      .ctx = ctx,
> > +                                      .flags = IGT_SPIN_POLL_RUN);
> > +             spin[1] = __igt_spin_new(i915,
> > +                                      .ctx = ctx,
> > +                                      .dependency = scratch);
> > +
> > +             igt_spin_busywait_until_started(spin[0]);
> > +
> > +             /* Running: actual class */
> > +             busy.handle = spin[0]->handle;
> > +             do_ioctl(i915, DRM_IOCTL_I915_GEM_BUSY, &busy);
> > +             igt_assert_eq_u32(busy.busy, 1u << (class + 16));
> > +
> > +             /* Queued(read): expected class */
> > +             busy.handle = spin[1]->handle;
> > +             do_ioctl(i915, DRM_IOCTL_I915_GEM_BUSY, &busy);
> > +             igt_assert_eq_u32(busy.busy, 1u << (class + 16));
> > +
> > +             /* Queued(write): expected class */
> > +             busy.handle = scratch;
> > +             do_ioctl(i915, DRM_IOCTL_I915_GEM_BUSY, &busy);
> > +             igt_assert_eq_u32(busy.busy,
> > +                               (1u << (class + 16)) | (class + 1));
> > +
> > +             igt_spin_free(i915, spin[1]);
> > +             igt_spin_free(i915, spin[0]);
> > +
> > +             gem_context_destroy(i915, ctx);
> > +     }
> > +
> > +     gem_close(i915, scratch);
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static int add_pmu(int pmu, const struct i915_engine_class_instance *ci)
> > +{
> > +     return perf_i915_open_group(I915_PMU_ENGINE_BUSY(ci->engine_class,
> > +                                                      ci->engine_instance),
> > +                                 pmu);
> > +}
> > +
> > +static void full(int i915, unsigned int flags)
> > +#define PULSE 0x1
> > +#define LATE 0x2
> > +{
> > +     struct drm_i915_gem_exec_object2 batch = {
> > +             .handle = batch_create(i915),
> > +     };
> > +
> > +     if (flags & LATE)
> > +             igt_require_sw_sync();
> > +
> > +     /*
> > +      * I915_CONTEXT_PARAM_ENGINE changes the meaning of I915_EXEC_DEFAULT
> > +      * to provide an automatic selection from the ctx->engine[]. It
> > +      * employs load-balancing to evenly distribute the workload the
> 
> The leading section needs rewritting for truth. It is the load balance 
> extensions which _can_ redefine the meanign of I915_EXEC_DEFAULT etc.. 
> I'm sure I didn't need to explain, but have just to make it clear which 
> part I am complaining about. :)

Hey, remember this is 2018!

> > +      * array. If we submit N spinners, we expect them to be simultaneously
> > +      * running across N engines and use PMU to confirm that the entire
> > +      * set of engines are busy.
> 
> Clarify it is only if using N contexts.
> 
> > +      *
> > +      * We complicate matters by interpersing shortlived tasks to challenge
> > +      * the kernel to search for space in which to insert new batches.
> > +      */
> > +
> > +
> > +     for (int mask = 0; mask < 32; mask++) {
> > +             struct i915_engine_class_instance *ci;
> > +             igt_spin_t *spin = NULL;
> > +             IGT_CORK_FENCE(cork);
> > +             unsigned int count;
> > +             double load;
> > +             int fence = -1;
> > +             int *pmu;
> > +
> > +             ci = list_engines(i915, 1u << mask, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, mask);
> > +
> > +             pmu = malloc(sizeof(*pmu) * count);
> > +             igt_assert(pmu);
> > +
> > +             if (flags & LATE)
> > +                     fence = igt_cork_plug(&cork, i915);
> > +
> > +             pmu[0] = -1;
> > +             for (unsigned int n = 0; n < count; n++) {
> > +                     uint32_t ctx;
> > +
> > +                     pmu[n] = add_pmu(pmu[0], &ci[n]);
> > +
> > +                     if (flags & PULSE) {
> > +                             struct drm_i915_gem_execbuffer2 eb = {
> > +                                     .buffers_ptr = to_user_pointer(&batch),
> > +                                     .buffer_count = 1,
> > +                                     .rsvd2 = fence,
> > +                                     .flags = flags & LATE ? I915_EXEC_FENCE_IN : 0,
> > +                             };
> > +                             gem_execbuf(i915, &eb);
> > +                     }
> > +
> > +                     /*
> > +                      * Each spinner needs to be one a new timeline,
> > +                      * otherwise they will just sit in the single queue
> > +                      * and not run concurrently.
> > +                      */
> > +                     ctx = load_balancer_create(i915, ci, count);
> > +
> > +                     if (spin == NULL) {
> > +                             spin = __igt_spin_new(i915, .ctx = ctx);
> > +                     } else {
> > +                             struct drm_i915_gem_execbuffer2 eb = {
> > +                                     .buffers_ptr = spin->execbuf.buffers_ptr,
> > +                                     .buffer_count = spin->execbuf.buffer_count,
> > +                                     .rsvd1 = ctx,
> > +                                     .rsvd2 = fence,
> > +                                     .flags = flags & LATE ? I915_EXEC_FENCE_IN : 0,
> > +                             };
> > +                             gem_execbuf(i915, &eb);
> > +                     }
> > +
> > +                     gem_context_destroy(i915, ctx);
> > +             }
> > +
> > +             if (flags & LATE) {
> > +                     igt_cork_unplug(&cork);
> > +                     close(fence);
> > +             }
> > +
> > +             load = measure_min_load(pmu[0], count, 10000);
> > +             igt_spin_free(i915, spin);
> > +
> > +             close(pmu[0]);
> > +             free(pmu);
> > +
> > +             free(ci);
> > +
> > +             igt_assert_f(load > 0.90,
> > +                          "minimum load for %d x class:%d was found to be only %.1f%% busy\n",
> > +                          count, mask, load*100);
> > +             gem_quiescent_gpu(i915);
> > +     }
> > +
> > +     gem_close(i915, batch.handle);
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static void nop(int i915)
> > +{
> > +     struct drm_i915_gem_exec_object2 batch = {
> > +             .handle = batch_create(i915),
> > +     };
> > +
> > +     for (int mask = 0; mask < 32; mask++) {
> 
> s/mask/class/
> 
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +             uint32_t ctx;
> > +
> > +             ci = list_engines(i915, 1u << mask, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             if (count < 2) {
> > +                     free(ci);
> > +                     continue;
> 
> Benchamrk only subtest for real veng?

Sure, that's a bit of internal knowledge leaking.

> > +             }
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, mask);
> > +             ctx = load_balancer_create(i915, ci, count);
> > +
> > +             for (int n = 0; n < count; n++) {
> > +                     struct drm_i915_gem_execbuffer2 execbuf = {
> > +                             .buffers_ptr = to_user_pointer(&batch),
> > +                             .buffer_count = 1,
> > +                             .flags = n + 1,
> > +                             .rsvd1 = ctx,
> > +                     };
> > +                     struct timespec tv = {};
> > +                     unsigned long nops;
> > +                     double t;
> > +
> > +                     igt_nsec_elapsed(&tv);
> > +                     nops = 0;
> > +                     do {
> > +                             for (int r = 0; r < 1024; r++)
> > +                                     gem_execbuf(i915, &execbuf);
> > +                             nops += 1024;
> > +                     } while (igt_seconds_elapsed(&tv) < 2);
> > +                     gem_sync(i915, batch.handle);
> > +
> > +                     t = igt_nsec_elapsed(&tv) * 1e-3 / nops;
> > +                     igt_info("%x:%d %.3fus\n", mask, n, t);
> 
> Class in decimal is better I think.

But it's mask :-p

It's treated as just a number and not as a class identifier.

> And some descriptive labels to info messages would be good. Like 
> "individual engines", "virtual engine" etc.

It does describe the individual engines and their composites. The output
looks clear and concise. You may want mask translated to a string... but
this code is oblivious as to what mask actually is.

The way it is used definitely looks more like mask than class.

> > +             }
> > +
> > +             {
> > +                     struct drm_i915_gem_execbuffer2 execbuf = {
> > +                             .buffers_ptr = to_user_pointer(&batch),
> > +                             .buffer_count = 1,
> > +                             .rsvd1 = ctx,
> > +                     };
> > +                     struct timespec tv = {};
> > +                     unsigned long nops;
> > +                     double t;
> > +
> > +                     igt_nsec_elapsed(&tv);
> > +                     nops = 0;
> > +                     do {
> > +                             for (int r = 0; r < 1024; r++)
> > +                                     gem_execbuf(i915, &execbuf);
> > +                             nops += 1024;
> > +                     } while (igt_seconds_elapsed(&tv) < 2);
> > +                     gem_sync(i915, batch.handle);
> > +
> > +                     t = igt_nsec_elapsed(&tv) * 1e-3 / nops;
> > +                     igt_info("%x:* %.3fus\n", mask, t);
> > +             }
> > +
> > +
> > +             igt_fork(child, count) {
> > +                     struct drm_i915_gem_execbuffer2 execbuf = {
> > +                             .buffers_ptr = to_user_pointer(&batch),
> > +                             .buffer_count = 1,
> > +                             .flags = child + 1,
> > +                             .rsvd1 = gem_context_clone(i915, ctx,
> > +                                                        I915_CONTEXT_CLONE_ENGINES, 0),
> > +                     };
> > +                     struct timespec tv = {};
> > +                     unsigned long nops;
> > +                     double t;
> > +
> > +                     igt_nsec_elapsed(&tv);
> > +                     nops = 0;
> > +                     do {
> > +                             for (int r = 0; r < 1024; r++)
> > +                                     gem_execbuf(i915, &execbuf);
> > +                             nops += 1024;
> > +                     } while (igt_seconds_elapsed(&tv) < 2);
> > +                     gem_sync(i915, batch.handle);
> > +
> > +                     t = igt_nsec_elapsed(&tv) * 1e-3 / nops;
> > +                     igt_info("[%d] %x:%d %.3fus\n", child, mask, child, t);
> > +
> > +                     memset(&tv, 0, sizeof(tv));
> > +                     execbuf.flags = 0;
> > +
> > +                     igt_nsec_elapsed(&tv);
> > +                     nops = 0;
> > +                     do {
> > +                             for (int r = 0; r < 1024; r++)
> > +                                     gem_execbuf(i915, &execbuf);
> > +                             nops += 1024;
> > +                     } while (igt_seconds_elapsed(&tv) < 2);
> > +                     gem_sync(i915, batch.handle);
> > +
> > +                     t = igt_nsec_elapsed(&tv) * 1e-3 / nops;
> > +                     igt_info("[%d] %x:* %.3fus\n", child, mask, t);
> > +
> > +                     gem_context_destroy(i915, execbuf.rsvd1);
> > +             }
> > +
> > +             igt_waitchildren();
> > +
> > +             gem_context_destroy(i915, ctx);
> > +             free(ci);
> > +     }
> > +
> > +     gem_close(i915, batch.handle);
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static void ping(int i915, uint32_t ctx, unsigned int engine)
> > +{
> > +     struct drm_i915_gem_exec_object2 obj = {
> > +             .handle = batch_create(i915),
> > +     };
> > +     struct drm_i915_gem_execbuffer2 execbuf = {
> > +             .buffers_ptr = to_user_pointer(&obj),
> > +             .buffer_count = 1,
> > +             .flags = engine,
> > +             .rsvd1 = ctx,
> > +     };
> > +     gem_execbuf(i915, &execbuf);
> > +     gem_sync(i915, obj.handle);
> > +     gem_close(i915, obj.handle);
> > +}
> > +
> > +static void semaphore(int i915)
> > +{
> > +     uint32_t block[2], scratch;
> > +     igt_spin_t *spin[3];
> > +
> > +     /*
> > +      * If we are using HW semaphores to launch serialised requests
> > +      * on different engine concurrently, we want to verify that real
> > +      * work is unimpeded.
> > +      */
> > +     igt_require(gem_scheduler_has_preemption(i915));
> > +
> > +     block[0] = gem_context_create(i915);
> > +     block[1] = gem_context_create(i915);
> > +
> > +     scratch = gem_create(i915, 4096);
> > +     spin[2] = igt_spin_new(i915, .dependency = scratch);
> > +     for (int mask = 1; mask < 32; mask++) {
> 
> s/mask/class/ throughout.
> 
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count;
> > +             uint32_t vip;
> > +
> > +             ci = list_engines(i915, 1u << mask, &count);
> > +             if (!ci)
> > +                     continue;
> > +
> > +             if (count < ARRAY_SIZE(block))
> > +                     continue;
> > +
> > +             /* Ensure that we completely occupy all engines in this group */
> > +             count = ARRAY_SIZE(block);
> > +
> > +             for (int i = 0; i < count; i++) {
> > +                     set_load_balancer(i915, block[i], ci, count);
> > +                     spin[i] = __igt_spin_new(i915,
> > +                                                    .ctx = block[i],
> > +                                                    .dependency = scratch);
> 
> Alignment.
> 
> > +             }
> > +
> > +             /*
> > +              * Either we haven't blocked both engines with semaphores,
> > +              * or we let the vip through. If not, we hang.
> > +              */
> > +             vip = gem_context_create(i915);
> > +             set_load_balancer(i915, vip, ci, count);
> > +             ping(i915, vip, 0);
> > +             gem_context_destroy(i915, vip);
> > +
> > +             for (int i = 0; i < count; i++)
> > +                     igt_spin_free(i915, spin[i]);
> > +
> > +             free(ci);
> > +     }
> > +     igt_spin_free(i915, spin[2]);
> > +     gem_close(i915, scratch);
> > +
> > +     gem_context_destroy(i915, block[1]);
> > +     gem_context_destroy(i915, block[0]);
> > +
> > +     gem_quiescent_gpu(i915);
> > +}
> > +
> > +static void smoketest(int i915, int timeout)
> > +{
> > +     struct drm_i915_gem_exec_object2 batch[2] = {
> > +             { .handle = __batch_create(i915, 16380) }
> > +     };
> > +     unsigned int ncontext = 0;
> > +     uint32_t *contexts = NULL;
> > +     uint32_t *handles = NULL;
> > +
> > +     igt_require_sw_sync();
> > +
> > +     for (int mask = 0; mask < 32; mask++) {
> > +             struct i915_engine_class_instance *ci;
> > +             unsigned int count = 0;
> > +
> > +             ci = list_engines(i915, 1u << mask, &count);
> > +             if (!ci || count < 2) {
> > +                     free(ci);
> > +                     continue;
> > +             }
> > +
> > +             igt_debug("Found %d engines of class %d\n", count, mask);
> > +
> > +             ncontext += 128;
> > +             contexts = realloc(contexts, sizeof(*contexts) * ncontext);
> > +             igt_assert(contexts);
> > +
> > +             for (unsigned int n = ncontext - 128; n < ncontext; n++) {
> > +                     contexts[n] = load_balancer_create(i915, ci, count);
> > +                     igt_assert(contexts[n]);
> > +             }
> > +
> > +             free(ci);
> > +     }
> > +     igt_debug("Created %d virtual engines (one per context)\n", ncontext);
> > +     igt_require(ncontext);
> > +
> > +     contexts = realloc(contexts, sizeof(*contexts) * ncontext * 4);
> > +     igt_assert(contexts);
> > +     memcpy(contexts + ncontext, contexts, ncontext * sizeof(*contexts));
> > +     ncontext *= 2;
> > +     memcpy(contexts + ncontext, contexts, ncontext * sizeof(*contexts));
> > +     ncontext *= 2;
> > +
> > +     handles = malloc(sizeof(*handles) * ncontext);
> > +     igt_assert(handles);
> > +     for (unsigned int n = 0; n < ncontext; n++)
> > +             handles[n] = gem_create(i915, 4096);
> > +
> > +     igt_until_timeout(timeout) {
> > +             unsigned int count = 1 + (rand() % (ncontext - 1));
> > +             IGT_CORK_FENCE(cork);
> > +             int fence = igt_cork_plug(&cork, i915);
> > +
> > +             for (unsigned int n = 0; n < count; n++) {
> > +                     struct drm_i915_gem_execbuffer2 eb = {
> > +                             .buffers_ptr = to_user_pointer(batch),
> > +                             .buffer_count = ARRAY_SIZE(batch),
> > +                             .rsvd1 = contexts[n],
> > +                             .rsvd2 = fence,
> > +                             .flags = I915_EXEC_BATCH_FIRST | I915_EXEC_FENCE_IN,
> > +                     };
> > +                     batch[1].handle = handles[n];
> > +                     gem_execbuf(i915, &eb);
> > +             }
> > +             igt_permute_array(handles, count, igt_exchange_int);
> > +
> > +             igt_cork_unplug(&cork);
> > +             for (unsigned int n = 0; n < count; n++)
> > +                     gem_sync(i915, handles[n]);
> > +
> > +             close(fence);
> > +     }
> > +
> > +     for (unsigned int n = 0; n < ncontext; n++) {
> > +             gem_close(i915, handles[n]);
> > +             __gem_context_destroy(i915, contexts[n]);
> > +     }
> > +     free(handles);
> > +     free(contexts);
> > +     gem_close(i915, batch[0].handle);
> > +}
> > +
> > +static bool has_context_engines(int i915)
> > +{
> > +     struct drm_i915_gem_context_param p = {
> > +             .param = I915_CONTEXT_PARAM_ENGINES,
> > +     };
> > +
> > +     return __gem_context_set_param(i915, &p) == 0;
> > +}
> > +
> > +static bool has_load_balancer(int i915)
> > +{
> > +     struct i915_engine_class_instance ci = {};
> > +     uint32_t ctx;
> > +     int err;
> > +
> > +     ctx = gem_context_create(i915);
> > +     err = __set_load_balancer(i915, ctx, &ci, 1);
> > +     gem_context_destroy(i915, ctx);
> > +
> > +     return err == 0;
> > +}
> > +
> > +igt_main
> > +{
> > +     int i915 = -1;
> > +
> > +     igt_skip_on_simulation();
> > +
> > +     igt_fixture {
> > +             i915 = drm_open_driver(DRIVER_INTEL);
> > +             igt_require_gem(i915);
> > +
> > +             gem_require_contexts(i915);
> > +             igt_require(has_context_engines(i915));
> > +             igt_require(has_load_balancer(i915));
> > +
> > +             igt_fork_hang_detector(i915);
> > +     }
> > +
> > +     igt_subtest("invalid-balancer")
> > +             invalid_balancer(i915);
> > +
> > +     igt_subtest("individual")
> > +             individual(i915);
> > +
> > +     igt_subtest("indicies")
> > +             indicies(i915);
> > +
> > +     igt_subtest("busy")
> > +             busy(i915);
> > +
> > +     igt_subtest_group {
> > +             static const struct {
> > +                     const char *name;
> > +                     unsigned int flags;
> > +             } phases[] = {
> > +                     { "", 0 },
> > +                     { "-pulse", PULSE },
> > +                     { "-late", LATE },
> > +                     { "-late-pulse", PULSE | LATE },
> > +                     { }
> > +             };
> > +             for (typeof(*phases) *p = phases; p->name; p++)
> > +                     igt_subtest_f("full%s", p->name)
> > +                             full(i915, p->flags);
> > +     }
> > +
> > +     igt_subtest("nop")
> > +             nop(i915);
> > +
> > +     igt_subtest("semaphore")
> > +             semaphore(i915);
> > +
> > +     igt_subtest("smoke")
> > +             smoketest(i915, 20);
> > +
> > +     igt_fixture {
> > +             igt_stop_hang_detector();
> > +     }
> > +}
> > diff --git a/tests/meson.build b/tests/meson.build
> > index 7e0089e74..eeea3611d 100644
> > --- a/tests/meson.build
> > +++ b/tests/meson.build
> > @@ -288,6 +288,13 @@ test_executables += executable('gem_eio',
> >          install : true)
> >   test_list += 'gem_eio'
> >   
> > +test_executables += executable('gem_exec_balancer', 'i915/gem_exec_balancer.c',
> > +        dependencies : test_deps + [ lib_igt_perf ],
> > +        install_dir : libexecdir,
> > +        install_rpath : libexecdir_rpathdir,
> > +        install : true)
> > +test_progs += 'gem_exec_balancer'
> > +
> >   test_executables += executable('gem_mocs_settings',
> >          join_paths('i915', 'gem_mocs_settings.c'),
> >          dependencies : test_deps + [ lib_igt_perf ],
> > 
> 
> Regards,
> 
> Tvrtko
> 
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