Quoting Thomas Hellström (Intel) (2020-07-27 19:08:39)
>
> On 7/15/20 1:51 PM, Chris Wilson wrote:
> > Acquire all the objects and their backing storage, and page directories,
> > as used by execbuf under a single common ww_mutex. Albeit we have to
> > restart the critical section a few times in order to handle various
> > restrictions (such as avoiding copy_(from|to)_user and mmap_sem).
> >
> > Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> > ---
> > .../gpu/drm/i915/gem/i915_gem_execbuffer.c | 168 +++++++++---------
> > .../i915/gem/selftests/i915_gem_execbuffer.c | 8 +-
> > 2 files changed, 87 insertions(+), 89 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > index ebabc0746d50..db433f3f18ec 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c
> > @@ -20,6 +20,7 @@
> > #include "gt/intel_gt_pm.h"
> > #include "gt/intel_gt_requests.h"
> > #include "gt/intel_ring.h"
> > +#include "mm/i915_acquire_ctx.h"
> >
> > #include "i915_drv.h"
> > #include "i915_gem_clflush.h"
> > @@ -244,6 +245,8 @@ struct i915_execbuffer {
> > struct intel_context *context; /* logical state for the request */
> > struct i915_gem_context *gem_context; /** caller's context */
> >
> > + struct i915_acquire_ctx acquire; /** lock for _all_ DMA reservations
> > */
> > +
> > struct i915_request *request; /** our request to build */
> > struct eb_vma *batch; /** identity of the batch obj/vma */
> >
> > @@ -389,42 +392,6 @@ static void eb_vma_array_put(struct eb_vma_array *arr)
> > kref_put(&arr->kref, eb_vma_array_destroy);
> > }
> >
> > -static int
> > -eb_lock_vma(struct i915_execbuffer *eb, struct ww_acquire_ctx *acquire)
> > -{
> > - struct eb_vma *ev;
> > - int err = 0;
> > -
> > - list_for_each_entry(ev, &eb->submit_list, submit_link) {
> > - struct i915_vma *vma = ev->vma;
> > -
> > - err = ww_mutex_lock_interruptible(&vma->resv->lock, acquire);
> > - if (err == -EDEADLK) {
> > - struct eb_vma *unlock = ev, *en;
> > -
> > - list_for_each_entry_safe_continue_reverse(unlock, en,
> > -
> > &eb->submit_list,
> > -
> > submit_link) {
> > - ww_mutex_unlock(&unlock->vma->resv->lock);
> > - list_move_tail(&unlock->submit_link,
> > &eb->submit_list);
> > - }
> > -
> > - GEM_BUG_ON(!list_is_first(&ev->submit_link,
> > &eb->submit_list));
> > - err =
> > ww_mutex_lock_slow_interruptible(&vma->resv->lock,
> > - acquire);
> > - }
> > - if (err) {
> > - list_for_each_entry_continue_reverse(ev,
> > - &eb->submit_list,
> > - submit_link)
> > - ww_mutex_unlock(&ev->vma->resv->lock);
> > - break;
> > - }
> > - }
> > -
> > - return err;
> > -}
> > -
> > static int eb_create(struct i915_execbuffer *eb)
> > {
> > /* Allocate an extra slot for use by the sentinel */
> > @@ -668,6 +635,25 @@ eb_add_vma(struct i915_execbuffer *eb,
> > }
> > }
> >
> > +static int eb_lock_mm(struct i915_execbuffer *eb)
> > +{
> > + struct eb_vma *ev;
> > + int err;
> > +
> > + list_for_each_entry(ev, &eb->bind_list, bind_link) {
> > + err = i915_acquire_ctx_lock(&eb->acquire, ev->vma->obj);
> > + if (err)
> > + return err;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int eb_acquire_mm(struct i915_execbuffer *eb)
> > +{
> > + return i915_acquire_mm(&eb->acquire);
> > +}
> > +
> > struct eb_vm_work {
> > struct dma_fence_work base;
> > struct eb_vma_array *array;
> > @@ -1390,7 +1376,15 @@ static int eb_reserve_vm(struct i915_execbuffer *eb)
> > unsigned long count;
> > struct eb_vma *ev;
> > unsigned int pass;
> > - int err = 0;
> > + int err;
> > +
> > + err = eb_lock_mm(eb);
> > + if (err)
> > + return err;
> > +
> > + err = eb_acquire_mm(eb);
> > + if (err)
> > + return err;
> >
> > count = 0;
> > INIT_LIST_HEAD(&unbound);
> > @@ -1416,10 +1410,15 @@ static int eb_reserve_vm(struct i915_execbuffer *eb)
> > if (count == 0)
> > return 0;
> >
> > + /* We need to reserve page directories, release all, start over */
> > + i915_acquire_ctx_fini(&eb->acquire);
> > +
> > pass = 0;
> > do {
> > struct eb_vm_work *work;
> >
> > + i915_acquire_ctx_init(&eb->acquire);
>
> Couldn't we do a i915_acquire_ctx_rollback() here to avoid losing our
> ticket? That would mean deferring i915_acquire_ctx_done() until all
> potential rollbacks have been performed.
We need to completely drop the acquire-class for catching up with userptr
(and anything else deferred that doesn't meet the current fence semantics).
I thought it was sensible to drop all around the waits in this loop, and
tidier to always reacquire at the beginning of each loop.
> Or even better if we defer _ctx_done(), couldn't we just continue
> locking the pts here instead of dropping and re-acquiring everything?
Userptr would like to have word. If you just mean these do lines, then
yes fini/init is overkill -- it just looked simpler than doing it at the
end of the loop. The steady-state load is not meant to get past the
optimistic fastpath.
-Chris
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