Revert "drm/i915/gt: Wait for new requests in intel_gt_retire_requests()"

From inside an active timeline in the execbuf ioctl, we may try to
reclaim some space in the GGTT. We need GGTT space for all objects on
!full-ppgtt platforms, and for context images everywhere. However, to
free up space in the GGTT we may need to remove some pinned objects
(e.g. context images) that require flushing the idle barriers to remove.
For this we use the big hammer of intel_gt_wait_for_idle()

However, commit 7936a22dd466 ("drm/i915/gt: Wait for new requests in
intel_gt_retire_requests()") will continue spinning on the wait if a
timeline is active but lacks requests, as is the case during execbuf
reservation. Spinning forever is quite time consuming, so revert that
commit and start again.

In practice, the effect commit 7936a22dd466 was trying to achieve is
accomplished by commit 1683d24c1470 ("drm/i915/gt: Move new timelines
to the end of active_list"), so there is no immediate rush to replace
the looping.

Testcase: igt/gem_exec_reloc/basic-range
Fixes: a46bfdc83fee ("drm/i915/gt: Wait for new requests in intel_gt_retire_requests()")
References: 1683d24c1470 ("drm/i915/gt: Move new timelines to the end of active_list")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191121071044.97798-1-chris@chris-wilson.co.uk
(cherry picked from commit 689122dcc36e08f53732adf7ae0246f62eff3eb6)
[Joonas: Corrected Fixes: tag ref to match drm-intel-next-fixes]
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_requests.c b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
index ccbddddbbd524d697abc08a957ea8fd08c24eae4..353809ac275452dfe6d1a244da4991ed5588f9a9 100644 (file)
--- a/drivers/gpu/drm/i915/gt/intel_gt_requests.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_requests.c
@@ -33,6 +33,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
 {
        struct intel_gt_timelines *timelines = &gt->timelines;
        struct intel_timeline *tl, *tn;
+       unsigned long active_count = 0;
        unsigned long flags;
        bool interruptible;
        LIST_HEAD(free);
@@ -45,8 +46,10 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
 
        spin_lock_irqsave(&timelines->lock, flags);
        list_for_each_entry_safe(tl, tn, &timelines->active_list, link) {
-               if (!mutex_trylock(&tl->mutex))
+               if (!mutex_trylock(&tl->mutex)) {
+                       active_count++; /* report busy to caller, try again? */
                        continue;
+               }
 
                intel_timeline_get(tl);
                GEM_BUG_ON(!tl->active_count);
@@ -73,6 +76,8 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
                list_safe_reset_next(tl, tn, link);
                if (!--tl->active_count)
                        list_del(&tl->link);
+               else
+                       active_count += !!rcu_access_pointer(tl->last_request.fence);
 
                mutex_unlock(&tl->mutex);
 
@@ -87,7 +92,7 @@ long intel_gt_retire_requests_timeout(struct intel_gt *gt, long timeout)
        list_for_each_entry_safe(tl, tn, &free, link)
                __intel_timeline_free(&tl->kref);
 
-       return list_empty(&timelines->active_list) ? 0 : timeout;
+       return active_count ? timeout : 0;
 }
 
 int intel_gt_wait_for_idle(struct intel_gt *gt, long timeout)