Quoting Tvrtko Ursulin (2018-03-15 13:36:26)
>
> On 15/03/2018 13:14, Chris Wilson wrote:
> > Quoting Tvrtko Ursulin (2018-03-15 12:56:17)
> >> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >>
> >> More than one test assumes that the spinner is running pretty much
> >> immediately after we have create or submitted it.
> >>
> >> In actuality there is a variable delay, especially on execlists platforms,
> >> between submission and spin batch starting to run on the hardware.
> >>
> >> To enable tests which care about this level of timing to account for this,
> >> we add a new spin batch constructor which provides an output field which
> >> can be polled to determine when the batch actually started running.
> >>
> >> This is implemented via MI_STOREDW_IMM from the spin batch, writing into
> >> memory mapped page shared with userspace.
> >>
> >> Using this facility from perf_pmu, where applicable, should improve very
> >> occasional test fails across the set and platforms.
> >>
> >> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> >> Suggested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >> ---
> >> lib/igt_dummyload.c | 99 +++++++++++++++++++++++++++++++----
> >> lib/igt_dummyload.h | 9 ++++
> >> tests/perf_pmu.c | 145 +++++++++++++++++++++++++++++++++++-----------------
> >> 3 files changed, 196 insertions(+), 57 deletions(-)
> >>
> >> diff --git a/lib/igt_dummyload.c b/lib/igt_dummyload.c
> >> index 4b20f23dfe26..0447d2f14d57 100644
> >> --- a/lib/igt_dummyload.c
> >> +++ b/lib/igt_dummyload.c
> >> @@ -74,9 +74,12 @@ fill_reloc(struct drm_i915_gem_relocation_entry *reloc,
> >> reloc->write_domain = write_domains;
> >> }
> >>
> >> -static int emit_recursive_batch(igt_spin_t *spin,
> >> - int fd, uint32_t ctx, unsigned engine,
> >> - uint32_t dep, bool out_fence)
> >> +#define OUT_FENCE (1 << 0)
> >> +#define POLL_RUN (1 << 1)
> >> +
> >> +static int
> >> +emit_recursive_batch(igt_spin_t *spin, int fd, uint32_t ctx, unsigned engine,
> >> + uint32_t dep, unsigned int flags)
> >> {
> >> #define SCRATCH 0
> >> #define BATCH 1
> >> @@ -116,6 +119,8 @@ static int emit_recursive_batch(igt_spin_t *spin,
> >> execbuf.buffer_count++;
> >>
> >> if (dep) {
> >> + igt_assert(!(flags & POLL_RUN));
> >> +
> >
> > Challenge left to the reader :)
>
> Well not the reader, whoever gets to need both. :)
>
> >> /* dummy write to dependency */
> >> obj[SCRATCH].handle = dep;
> >> fill_reloc(&relocs[obj[BATCH].relocation_count++],
> >> @@ -123,6 +128,41 @@ static int emit_recursive_batch(igt_spin_t *spin,
> >> I915_GEM_DOMAIN_RENDER,
> >> I915_GEM_DOMAIN_RENDER);
> >> execbuf.buffer_count++;
> >> + } else if (flags & POLL_RUN) {
> >> + unsigned int offset;
> >> +
> >> + igt_assert(!dep);
> >> +
> >> + spin->poll_handle = gem_create(fd, 4096);
> >> + spin->running = __gem_mmap__wc(fd, spin->poll_handle,
> >> + 0, 4096, PROT_READ | PROT_WRITE);
> >
> > Use mmap_cpu and gem_set_caching().
>
> Wouldn't that get us into coherency issues on some platforms? I keep the
> page mapped for API users to poll on.
bxt-a? The point of using gem_set_caching() is that it is coherent with
the CPU cache even on !llc via snooping. It's then essentially the same
as how we handle breadcrumbs.
Now admittedly, we should do
if (__gem_set_caching() == 0)
running = __gem_mmap__wb();
else
running = __gem_mmap__wc();
The caller need be known the wiser; except having to assume the worst
and so __sync_synchronize() if they do *running = x themselves.
> >> + igt_assert(spin->running);
> >> + igt_assert_eq(*spin->running, 0);
> >> +
> >> + *batch++ = MI_STORE_DWORD_IMM | (gen < 6 ? 1 << 22 : 0);
> >
> > Hmm, have we forgot the (len-2) or is this an unusual command that knows
> > its own length?
>
> I lifted the code from elsewhere.
I checked, we have the same bug everywhere or nowhere. :|
> >> +/**
> >> + * igt_spin_batch_new_poll:
> >> + * @fd: open i915 drm file descriptor
> >> + * @engine: Ring to execute batch OR'd with execbuf flags. If value is less
> >> + * than 0, execute on all available rings.
> >> + *
> >> + * Start a recursive batch on a ring. Immediately returns a #igt_spin_t that
> >> + * contains the batch's handle that can be waited upon. The returned structure
> >> + * must be passed to igt_spin_batch_free() for post-processing.
> >> + *
> >> + * igt_spin_t->running will containt a pointer which target will change from
> >> + * zero to one once the spinner actually starts executing on the GPU.
> >> + *
> >> + * Returns:
> >> + * Structure with helper internal state for igt_spin_batch_free().
> >> + */
> >> +igt_spin_t *
> >> +igt_spin_batch_new_poll(int fd, uint32_t ctx, unsigned engine)
> >> +{
> >> + igt_spin_t *spin;
> >> +
> >> + igt_require_gem(fd);
> >> + igt_require(gem_mmap__has_wc(fd));
> >
> > igt_require(gem_can_store_dword(fd, engine));
> >
> > Not all platforms have a MI_STORE_DWORD/DATA_IMM (with virtual addresses
> > at least) and some platforms will die (*cough* snb *cough*).
>
> Grr that makes it all problematic. Well, maybe not completely, I can
> just fall back to less accurate method on those platforms.
It's only a few, I don't think in the grand scheme of things it's enough
to worry about. We should lose just a few pmu tests on snb.
> >> static void
> >> __submit_spin_batch(int gem_fd,
> >> + igt_spin_t *spin,
> >> struct drm_i915_gem_exec_object2 *obj,
> >> const struct intel_execution_engine2 *e)
> >> {
> >> struct drm_i915_gem_execbuffer2 eb = {
> >> - .buffer_count = 1,
> >> .buffers_ptr = to_user_pointer(obj),
> >> .flags = e2ring(gem_fd, e),
> >> };
> >>
> >> + if (spin->running) {
> >> + obj[0].handle = spin->poll_handle;
> >> + obj[0].flags = EXEC_OBJECT_ASYNC;
> >> + obj[1].handle = spin->handle;
> >> + eb.buffer_count = 2;
> >> + } else {
> >> + obj[0].handle = spin->handle;
> >> + eb.buffer_count = 1;
> >> + }
> >
> > obj[] must be set up by the caller; the EXEC_OBJECT_PINNED are
> > essential. Or else the kernel *will* move spin->poll_handle and then it
> > is fubar.
>
> Why the caller has to do it? It is providing obj array which gets
> populated by the helper and by the kernel. If I add EXEC_OBJECT_PINNED
> to the helper is there a remaining problem?
Yes. The caller needs to ensure that flags = PINNED *and* the offset is
correct. We can't just randomly stuff PINNED in there as that pretty
much guarantees the object will be moved, breaking the implicit
relocations.
As we are making changes to igt_spin_t, one of the ideas was that we put
the obj[] array there (with the offsets and flags setup correctly) so
that we could just feed that in again later without having to worry
about the relocations.
-Chris
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